fix: checkout repo in Test Report so test-reporter can list tracked files

[Arthurvdv]

Problem

The Test Report workflow (test-report.yml, introduced in #345 / commit 6e14a0d) runs via workflow_run without checking out the repository. It downloads the per-version test-results-* artifacts with a manual download-artifact step (merge-multiple: true) to build a single unified report, then passes only path: to dorny/test-reporter.

dorny/test-reporter only uses the GitHub REST API to list tracked files (for resolving source paths in failure annotations) when it downloads the artifact via the artifact: input. With the manual-download + path: setup it falls back to git ls-files, which fails:

Listing all files tracked by git
  /usr/bin/git ls-files -z
  fatal: not a git repository (or any of the parent directories): .git
Error: The process '/usr/bin/git' failed with exit code 128

Because test-report.yml runs from main, this currently fails for every PR.

Fix

Add an actions/checkout@v6 step before the artifact download, pinned to workflow_run.head_sha, so:

• git ls-files finds a repository, and
• annotations resolve against the exact tested commit (including new files in fork PRs).

The single unified report behavior is preserved (no switch to the per-artifact artifact: input).

Notes

• Checkout runs before download-artifact so its default cleaning does not remove the downloaded TestResults.
• Only contents: read is needed, which the job already grants.

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com