ci: cancel superseded test runs with concurrency groups

[Wuodan]

Use concurrency groups based on the workflow and PR number or Git ref.
Cancel an in-progress run when a newer run uses the same group, freeing CI capacity from outdated tests.

Release events use a separate suffix to keep them distinct where applicable.

[Wuodan]

Update:
This now gives release-triggered runs a separate suffix in the group name.

This workflow is not release-triggered, but I use these concurrency settings in many repos and workflows and will suggest these in other bats-repos too.
And then it's just nice to have the same lines everywhere without having to think about the details.