Repository: godot
Issue: NuGet error "UntrustedRoot: self signed certificate in certificate chain"
Labels: bug,topic:editor,needs testing,topic:dotnet

**Godot version:**
v3.3.stable.mono.official

**OS/device including version:**
Pop!_OS 20.10

**Issue description:**
I am almost entirely sure this is due to a mistake on my end, as I am very new to game development on Godot and C# on Linux. When attempting to run my first Godot project using C#, I run into a set of NuGet-related bugs. I apologize if this is a simple bug to fix, I am rather new to Godot, though I could not find any references to the same issue related to it. Help is very much appreciated! 😄 

```
Build started 5/6/2021 9:03:28 PM.
     1>Project "/home/alec/Programming/Projects/Project Spirits/Project Spirits.sln" on node 1 (Restore target(s)).
     1>ValidateSolutionConfiguration:
         Building solution configuration "Debug|Any CPU".
       Restoring packages for /tmp/NuGetScratch/ea34b7eef7bb48759d935f3c2e24af33/6cb09316d5954756ad55e825d5aa4b94.proj...
         CACHE https://api.nuget.org/v3-flatcontainer/godot.net.sdk/index.json
         CACHE https://api.nuget.org/v3-flatcontainer/godot.net.sdk/3.3.0/godot.net.sdk.3.3.0.nupkg
       Installing Godot.NET.Sdk 3.3.0.
       Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': Signature Hash Algorithm: SHA256
       Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': Timestamp: 3/16/2021 3:43:52 PM
       
       Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': Verifying repository primary signature's timestamp with timestamping service certificate: 
         Subject Name: CN=Symantec SHA256 TimeStamping Signer - G3, OU=Symantec Trust Network, O=Symantec Corporation, C=US
         SHA1 hash: A9A4121063D71D48E8529A4681DE803E3E7954B0
         SHA256 hash: C474CE76007D02394E0DA5E4DE7C14C680F9E282013CFEF653EF5DB71FDF61F8
         Issued by: CN=Symantec SHA256 TimeStamping CA, OU=Symantec Trust Network, O=Symantec Corporation, C=US
         Valid from: 12/22/2017 5:00:00 PM to 3/22/2029 4:59:59 PM
       
       Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': Signature type: Repository
       Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': nuget-v3-service-index-url: https://api.nuget.org/v3/index.json
       Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': nuget-package-owners: neikeq
       Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': Verifying the repository primary signature with certificate: 
         Subject Name: CN=NuGet.org Repository by Microsoft, O=NuGet.org Repository by Microsoft, L=Redmond, S=Washington, C=US
         SHA1 hash: 8FB6D7FCF7AD49EB774446EFE778B33365BB7BFB
         SHA256 hash: 0E5F38F57DC1BCC806D8494F4F90FBCEDD988B46760709CBEEC6F4219AA6157D
         Issued by: CN=DigiCert SHA2 Assured ID Code Signing CA, OU=www.digicert.com, O=DigiCert Inc, C=US
         Valid from: 4/9/2018 5:00:00 PM to 4/14/2021 5:00:00 AM
       
     0>/home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj : error : Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': The repository primary signature's timestamp found a chain building issue: UntrustedRoot: self signed certificate in certificate chain
     0>/home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj : error : Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': The repository primary signature validity period has expired.
     1>/home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj : warning NU1503: Skipping restore for project '/home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj'. The project file may be invalid or missing targets required for restore. [/home/alec/Programming/Projects/Project Spirits/Project Spirits.sln]
       _GetAllRestoreProjectPathItems:
         Determining projects to restore...
     1>/usr/share/dotnet/sdk/5.0.100/NuGet.targets(131,5): warning : Unable to find a project to restore! [/home/alec/Programming/Projects/Project Spirits/Project Spirits.sln]
     1>Done Building Project "/home/alec/Programming/Projects/Project Spirits/Project Spirits.sln" (Restore target(s)).
   1:2>Project "/home/alec/Programming/Projects/Project Spirits/Project Spirits.sln" on node 1 (Build target(s)).
     1>ValidateSolutionConfiguration:
         Building solution configuration "Debug|Any CPU".
       Restoring packages for /tmp/NuGetScratch/fe6d0cee89ba477dab68b4ef4352c084/d62d62fb864349858782b89de9947ed2.proj...
         CACHE https://api.nuget.org/v3-flatcontainer/godot.net.sdk/index.json
         CACHE https://api.nuget.org/v3-flatcontainer/godot.net.sdk/3.3.0/godot.net.sdk.3.3.0.nupkg
       Installing Godot.NET.Sdk 3.3.0.
       Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': Signature Hash Algorithm: SHA256
       Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': Timestamp: 3/16/2021 3:43:52 PM
       
       Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': Verifying repository primary signature's timestamp with timestamping service certificate: 
         Subject Name: CN=Symantec SHA256 TimeStamping Signer - G3, OU=Symantec Trust Network, O=Symantec Corporation, C=US
         SHA1 hash: A9A4121063D71D48E8529A4681DE803E3E7954B0
         SHA256 hash: C474CE76007D02394E0DA5E4DE7C14C680F9E282013CFEF653EF5DB71FDF61F8
         Issued by: CN=Symantec SHA256 TimeStamping CA, OU=Symantec Trust Network, O=Symantec Corporation, C=US
         Valid from: 12/22/2017 5:00:00 PM to 3/22/2029 4:59:59 PM
       
       Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': Signature type: Repository
       Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': nuget-v3-service-index-url: https://api.nuget.org/v3/index.json
       Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': nuget-package-owners: neikeq
       Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': Verifying the repository primary signature with certificate: 
         Subject Name: CN=NuGet.org Repository by Microsoft, O=NuGet.org Repository by Microsoft, L=Redmond, S=Washington, C=US
         SHA1 hash: 8FB6D7FCF7AD49EB774446EFE778B33365BB7BFB
         SHA256 hash: 0E5F38F57DC1BCC806D8494F4F90FBCEDD988B46760709CBEEC6F4219AA6157D
         Issued by: CN=DigiCert SHA2 Assured ID Code Signing CA, OU=www.digicert.com, O=DigiCert Inc, C=US
         Valid from: 4/9/2018 5:00:00 PM to 4/14/2021 5:00:00 AM
       
     0>/home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj : error : Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': The repository primary signature's timestamp found a chain building issue: UntrustedRoot: self signed certificate in certificate chain
     0>/home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj : error : Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': The repository primary signature validity period has expired.
   1:2>Project "/home/alec/Programming/Projects/Project Spirits/Project Spirits.sln" (1:2) is building "/home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj" (2:2) on node 1 (default targets).
     2>/home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj : error MSB4236: The SDK 'Godot.NET.Sdk/3.3.0' specified could not be found.
     2>Done Building Project "/home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj" (default targets) -- FAILED.
     1>Done Building Project "/home/alec/Programming/Projects/Project Spirits/Project Spirits.sln" (Build target(s)) -- FAILED.

Build FAILED.

       "/home/alec/Programming/Projects/Project Spirits/Project Spirits.sln" (Restore target) (1) ->
       (_FilterRestoreGraphProjectInputItems target) -> 
         /home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj : warning NU1503: Skipping restore for project '/home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj'. The project file may be invalid or missing targets required for restore. [/home/alec/Programming/Projects/Project Spirits/Project Spirits.sln]


       "/home/alec/Programming/Projects/Project Spirits/Project Spirits.sln" (Restore target) (1) ->
       (Restore target) -> 
         /usr/share/dotnet/sdk/5.0.100/NuGet.targets(131,5): warning : Unable to find a project to restore! [/home/alec/Programming/Projects/Project Spirits/Project Spirits.sln]


         /home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj : error : Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': The repository primary signature's timestamp found a chain building issue: UntrustedRoot: self signed certificate in certificate chain
         /home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj : error : Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': The repository primary signature validity period has expired.


         /home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj : error : Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': The repository primary signature's timestamp found a chain building issue: UntrustedRoot: self signed certificate in certificate chain
         /home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj : error : Package 'Godot.NET.Sdk 3.3.0' from source 'https://api.nuget.org/v3/index.json': The repository primary signature validity period has expired.


       "/home/alec/Programming/Projects/Project Spirits/Project Spirits.sln" (Build target) (1:2) ->
       "/home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj" (default target) (2:2) ->
         /home/alec/Programming/Projects/Project Spirits/Project Spirits.csproj : error MSB4236: The SDK 'Godot.NET.Sdk/3.3.0' specified could not be found.

```

**Steps to reproduce:**
1) Create a new Godot project.
2) Create a 3D scene and C# script.
3) Input some code into the script.
4) Hit the run button at the top right.

**Minimal reproduction project:**
Just a note, the code is not functional. It's purposefully meant to NOT be and has multiple intentional bugs and mistakes (e.g. syntax errors, type-checking errors, and a typo) to see how Godot outputs errors and if it's worth it to link an external editor in.
[Project_Spirits.zip](https://github.com/godotengine/godot/files/6438978/Project_Spirits.zip)