Repository: godot
Issue: Custom Resources that worked in 4.2.2 do not in 4.3 (does not recognize as resource?)
Labels: bug,topic:gdscript,regression

### Tested versions

No issue in v4.2.2.stable.official [15073afe3] and previous
First visual(?) errors in v4.3.rc1.official [e343dbbcc]
First game-ending exception occurs in v4.3.rc2.official [3978628c6] and later (rc3 and 4.3 tested)

### System information

Godot v4.3.stable - Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1080 (NVIDIA; 32.0.15.6081) - Intel(R) Core(TM) i5-7600 CPU @ 3.50GHz (4 Threads)

### Issue description

Short version, something's wacky with my custom resources since I updated to 4.3 from 4.2.2

I have a very simple resource which looks like this:
```
class_name Infusion
extends Resource

@export var air: int = 0
@export var earth: int = 0
@export var fire: int = 0
@export var ice: int = 0
```
Which is used by another custom resource (CombatCard) as an export variable, like so:
`@export var infusion:= Infusion.new()`

In 4.2.2, this worked as I expected, with CombatCards that did not have a custom Infusion set defaulting to a new Infusion instance with 0s across the board. Additionally, the autocomplete had that custom resource icon (the cube thing) for the resources, as shown.
![image](https://github.com/user-attachments/assets/9f3ac46c-2fb4-48bf-a065-d680d21df86b)

This is not the case when I load that same project in 4.3.rc1 or later:
![image](https://github.com/user-attachments/assets/761d5f8a-12cd-401e-ba09-48e3e4c22d9f)

You'll notice that the Infusion resource (which extends Resource) has no symbol. Additionally, QuestInfoScreen now shows the icon for ColorRect, which is what that class extends, whereas previously it also had the cube icon. I don't know if that's intentional.

The project still seems to run fine despite this in 4.3.rc1. In 4.3.rc2, rc3, or 4.3, however, it causes the project to crash when run with the following error.

![image](https://github.com/user-attachments/assets/ef532135-5898-43f9-8517-66a69f7cf50d)
![image](https://github.com/user-attachments/assets/1b84d41a-a065-4408-a4ea-5fb71516592e)
```
Invalid call. Nonexistent function 'new' in base 'GDScript'
at function: @implicit_new
```

### Steps to reproduce

I've been able to reproduce the visual portion of this issue in a brand new project (here, MyCustomResource is another dead simple class that extends Resource and has a single member variable of type int, not even exported)
![image](https://github.com/user-attachments/assets/fc74042e-bf53-4f2b-8d8a-aa31e27b951b)

I've not been able to reproduce the crash yet. I suspect it has something to do with loading or preloading of the parent CombatCard resource, or scenes which use that resource? I don't really know, feel free to ask if you want more info.

My next plan is to try removing the Infusion class and just storing those variables in the parent resource, and see whether anything else is broken. I should also have access to Linux Mint in the short term to check if it's OS related.

If you think an MRP would help, I can try to pare down my main project a bit and upload that. I'm open to suggestions, if there's anything I can do to help let me know, in the meantime I'll carry on development in 4.2.2

### Minimal reproduction project (MRP)
[95789MRP.zip](https://github.com/user-attachments/files/16669153/95789MRP.zip)

EDIT: Did some hacking and slashing on the project, and got an MRP. It probably won't run _well_, but the important thing is that it results in the issue for me (before any other issue, anyway)

Step 1: Open Project
Step 2: Run Project

Project will throw the error before showing the main menu