Problem

The test project uses xUnit v2, which lacks proper support for conditionally skipping tests. There are 20+ tests across the repo that are only applicable on specific platforms (e.g., Windows-only windowsdesktop runtime tests). Currently these use early-return patterns with RuntimeInformation.IsOSPlatform() checks, which causes the tests to appear as passed in test results rather than skipped.

This is misleading — it inflates the passing test count and makes it harder to understand actual test coverage per platform. For example, windowsdesktop runtime tests early-return on Linux/macOS but show as green, giving the impression they ran successfully.

Additionally, PR #697 is adding platform-specific tests (Windows tar.gz extraction, Linux bash symlink preservation) that would also benefit from proper skip semantics.

Why xUnit v3

xUnit v3 has first-class support for dynamically skipping tests via Skip.If() / Skip.When() and the ITestCondition interface. Tests skipped this way appear as skipped in test results rather than passed, giving accurate visibility into what actually ran on each platform.

Scope

• Update xunit and related package references to v3
• Replace early-return platform checks with xUnit v3 skip APIs
• Affected files include AkaMsLinksTests.cs (9 occurrences), GivenThatIWantToGetTheSdkLinksFromAScript.cs (8), and GivenThatIWantToInstallDotnetFromAScript.cs (3)