Disable IJW tests on Windows 7. (dotnet/coreclr#22779)

Disable IJW tests on Windows 7. (dotnet/coreclr#22779)

Windows 7 loads desktop mscoree.dll when loading System.Private.CoreLib, before we can load our fake mscoree. So, when IJW modules are loaded, they load the real mscoree.dll, which breaks coreclr's IJW loading. Once we have true .NET Core IJW support in the MSVC++ compiler and .NET Core, then we'll be able to reenable these tests on Win7.

Fixes dotnet/coreclr#21796.

cc: @RussKeldorph @echesakovMSFT

Commit migrated from https://github.com/dotnet/coreclr/commit/3984fc9b98770289def807e1953533bc4a28781a