Get GitHub to recognize this repo as a C# repo

Today the PowerShell repo appears as "VHDL" in GitHub, incorrectly tagging it due to the size of the VHD test images inside the repo being counted by Linguist. Per looking through linguist to find the best solution, a 'vendor' folder within test will help it update the stats properly.

There are a lot of other test folder structures as well, but unfortunately they require being at the root, ruining some of the compartmentalization that is in place today.

Creating a PR so that I can make sure the tests still function fine.