Follow-up to a89183e638, which was
reverted in e4c4a178aa because a change
to the workflow trigger resulted in the PR branch not being checked out.
We used this opportunity to reimplement the coverage tracing and coverage
commenting in a two-workflow pattern with more granular permissions.
To reduce duplicative workflows, we removed the existing python test workflow
on PRs, at least until we run more distinct configurations on GitHub actions. The
run with coverage tracing enabled is sufficient for now. The existing workflow still
runs on pushes to main. We can revisit when adding more test configurations.
