Flaky Tests Due To Build Acceleration

[warappa]

Some UDX tests fail (on my machine) every second time as there seems to be multiple initialized instances of cached SchemaSet depending on the AppDomain of the executing test.
If it is initialized by a test with UDXs defined, then validation works. If it was initialized without it those UDX tests fail.

[warappa]

After hours of investigation of one test relyably toggling between Success and Failed, it turns out it is not about cached SchemaSet instances.
The flaky test Can_validate_Order_with_UDX_with_error is flaky because of Build Acceleration, which is enabled by default in VS 2022 17.9 Preview 2.0.
Disabling Build Acceleration in VS options fixes the problem.

Seems to be this issue:
dotnet/project-system#9001