Fix race condition in bump-requirements

[TheTripleV]

If the workflow runs concurrently, then the git push in this step or the Bump Version and push Tag in robotpy-meta could fail.

[auscompgeek]

Any ideas on how we can go about this? Does GitHub Actions have a way to limit the concurrency of a workflow?

[TheTripleV]

Oooh they added it in in April: https://docs.github.com/en/actions/learn-github-actions/workflow-syntax-for-github-actions#concurrency