ci: run module tests on Windows PowerShell 5.1 in shared workflow

[tablackburn]

Summary

Adds a dedicated test_powershell job to the shared ModuleCI.yml that builds and runs the full test suite under Windows PowerShell 5.1 (Desktop), alongside the existing PowerShell 7+ matrix (ubuntu/windows/macOS).

Desktop is not a runner OS, so it runs as its own job on windows-latest using the built-in powershell shell:

test_powershell:
  name: Run Tests (Windows PowerShell 5.1)
  runs-on: windows-latest
  steps:
    - uses: actions/checkout@v4
    - name: Test
      shell: powershell
      run: ./build.ps1 -Task Test -Bootstrap
    - name: Upload Unit Test Results
      ...

Its results are wired into publish-test-results (needs: [test, test_powershell]).

Motivation

Modules that declare Windows PowerShell (Desktop) support need the lowest supported engine exercised by CI, not just PowerShell 7+. PowerShellBuild 0.8.0 shipped a PS7-only ternary that broke module import on 5.1, and the pwsh-only test run did not catch it (psake/PowerShellBuild#126).

Notes / compatibility

• The existing test job (id and Run Pwsh Tests name) is unchanged, so no required-status-check names change for current consumers.
• The new 5.1 job runs unconditionally. No psake repo currently consumes this reusable workflow via uses: yet — fix: restore Windows PowerShell 5.1 import compatibility PowerShellBuild#126 is the first adopter — so blast radius today is limited to that PR.
• If a future consumer does not support Desktop, we can gate this job behind a workflow_call input; left unconditional for now per maintainer direction.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds a dedicated Windows PowerShell 5.1 test job to CI and wires it into the unit test results publishing flow.

Changes:

• Add a test_powershell job that runs tests under Windows PowerShell 5.1 (shell: powershell) on windows-latest.
• Update publish-test-results to depend on both test and test_powershell jobs.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.