Avoid having multiple test assets in a single test class

[Youssef1313]

Continuation of #7552.

Overrides of GetAssetsToGenerate should have no reason to provide multiple assets. Having multiple assets means that all of these will be built during class initialize, reducing the ability to run more stuff in parallel, and forcing the build of irrelevant assets when running a single test that uses one of those assets. Currently, the only test class with multiple assets is test\IntegrationTests\MSTest.Acceptance.IntegrationTests\TimeoutTests.cs