Merge branch 'js/ci-discard-prove-state' into maint-2.43

Merge branch 'js/ci-discard-prove-state' into maint-2.43

The way CI testing used "prove" could lead to running the test
suite twice needlessly, which has been corrected.

* js/ci-discard-prove-state:
  ci: avoid running the test suite _twice_
  ci: add support for GitLab CI
  ci: install test dependencies for linux-musl
  ci: squelch warnings when testing with unusable Git repo
  ci: unify setup of some environment variables
  ci: split out logic to set up failed test artifacts
  ci: group installation of Docker dependencies
  ci: make grouping setup more generic
  ci: reorder definitions for grouping functions