[RuntimeAsync] Disable building async tests on configurations that are not yet supported.

[VSadov]

Test-only change to disable building async tests on configurations that are not yet supported.

[Copilot]

Pull Request Overview

This PR adds a conditional DisableProjectBuild setting to skip building async tests on configurations (mono, nativeaot, wasm) that aren’t yet supported.

• Introduce a new <PropertyGroup> with a DisableProjectBuild conditioned on RuntimeFlavor, TestBuildMode, or TargetArchitecture.
• Retain the existing unconditional DisableProjectBuild for overall runtime async NYI.

Comments suppressed due to low confidence (1)

src/tests/async/Directory.Build.targets:9

• The unconditional <DisableProjectBuild> in the second PropertyGroup will override the conditional property above, effectively disabling builds for all configurations. Consider merging these into one PropertyGroup with an appropriate condition or removing the unconditional flag so supported configurations can build.

<DisableProjectBuild>true</DisableProjectBuild>

[VSadov]

The reason why we cannot just exclude the tests from running is because in some cases just trying to build is enough to cause failures as the post-build tooling may not be familiar with runtime async patterns.

For an example on how wasm gets broken if tries to build these tests see: #115947 (comment)

I think it makes sense to not even build these tests on configs where we do not yet expect them to work.

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[agocke]

LGTM, thanks!

[VSadov]

/ba-g two failures in threading and loader look like known and unrelated.