Exclude desktop-only Security test from mobile builds

[davidnguyen-tech]

Summary

• exclude SslAuthenticationOptionsTests.Desktop.cs from all mobile builds
• use TargetsMobile because tvOS builds this project as net11.0-unix, making the previous TargetPlatformIdentifier == 'unix' condition ineffective

Follow-up to #131922 and #132277.

Validation

• ./build.sh clr+libs -rc release
• System.Net.Security.Unit.Tests: 134 total, 0 failed, 3 skipped
• MSBuild compile matrix: excluded on tvOS, Android, and browser; included on Linux, macOS, and Windows
• fixed tvOS build binlog contains no SslAuthenticationOptionsTests.Desktop.cs compile input

Note

This pull request was prepared with GitHub Copilot assistance and reviewed by the submitting developer.

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[davidnguyen-tech]

/azp run runtime

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[davidnguyen-tech]

/azp run runtime-extra-platforms

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[Copilot]

Pull request overview

This PR updates the build condition for System.Net.Security.Unit.Tests so a desktop-only test file (SslAuthenticationOptionsTests.Desktop.cs) is excluded from mobile (and related) build legs, preventing it from being compiled where it can trigger startup failures.

Changes:

• Switch the SslAuthenticationOptionsTests.Desktop.cs Compile condition from TargetPlatformIdentifier-based checks to TargetsMobile-based gating.
• Ensure tvOS builds (which can build this project as net11.0-unix) still treat the build as “mobile” for exclusion purposes.

[davidnguyen-tech]

/azp run runtime-extra-platforms

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[jkotas]

This justification does not make sense. R2R IL-body stripping should not be stripping IL for generic instantiations.

Is this just trying to hide a real product bug in R2R?

[davidnguyen-tech]

That's a good point. If it's a bug in R2R, I think we should keep #131922 opened as a KBE until it's properly fixed, instead of closing it after just disabling the failing test. This way we don't block the CI while still tracking the bug.

cc @rzikm