Fix Internal Tests paths filter checkout

[clockwork-labs-bot]

What changed

Adds an explicit checkout step before dorny/paths-filter in the Internal Tests workflow.

Why

dorny/paths-filter@v3 needs a git working tree for push events. The Internal Tests workflow ran it before any checkout, so every push run on master failed immediately in Detect non-docs changes with:

fatal: not a git repository (or any of the parent directories): .git

This only showed up consistently on master because those runs are push events. On pull_request events, dorny/paths-filter can use the GitHub pull request files API with the PR number, so it does not need a local checkout for the same file detection path.

Adding checkout gives the action a repository when it handles push events, while leaving PR behavior unchanged.

Testing

• git diff --check
• PR Fix Internal Tests paths filter checkout #5295 Internal Tests job completed Checkout and Detect non-docs changes successfully, then moved on to private dispatch/wait.