Pin gha-setup-swift to v0.5.0 in the Windows workflow

[Kyle-Ye]

Summary

Pin compnerd/gha-setup-swift to v0.5.0 in the Windows workflow instead of tracking @main. @main currently points at the same commit as v0.5.0 (bbae8ce), so this doesn't change behavior. It only stops the job from picking up new action versions implicitly.

Investigation

The Windows job failed twice on 2026-09-28, both between 15:40 and 16:30 UTC:

• main (run 36451099513): the action's own swift --version check exited with code 1 without printing anything, not even the action's own error messages.
• Add Android CI that runs the tests on an emulator #30 (first attempt): that check succeeded, but the next step, swift test, reported swift as not recognized. Both steps had identical environment variables.

Neither the action version nor anything in this repository appears to be the cause:

• The same action commit passed the 12 Windows runs before the failures, the re-run of Add Android CI that runs the tests on an emulator #30, and all 24 diagnostic jobs below.
• v0.4.1 and v0.5.0 differ only in how the action exports Path. The runner applies GITHUB_PATH the same way to every step, so that change can't make swift disappear between two steps with identical environments.

The failures look like a transient problem on the runners at that time. There's no sign that pinning v0.4.1 would avoid them, and v0.4.1 adds every Path entry twice.

Diagnostics

A temporary commit (3c43b70, dropped from this PR) ran six identical Windows jobs four times, 24 jobs in total. Each job recorded the Swift setup state after installing Swift and again after swift test. All 24 passed. A typical report:

• The runner image is windows-2025-vs2026 20260922.246.2, the same as in both failures.
• Path has 73 entries, including the Swift toolchain and runtime directories, which are also in the user Path in the registry. SDKROOT is set.
• swift resolves to …\Toolchains\6.3.3+Asserts\usr\bin\swift.exe, and swift --version works.
• The installer exits with 0x0 without rolling back, and Defender real-time protection is off.

If the failure comes back, cherry-pick 3c43b70 to capture the same data on a failing runner.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.32%. Comparing base (6fd3c58) to head (930b1c6).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #32   +/-   ##
=======================================
  Coverage   96.32%   96.32%           
=======================================
  Files         108      108           
  Lines        8100     8100           
=======================================
  Hits         7802     7802           
  Misses        298      298           

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