Follow-up from #29534:

By specially named tags, a developer could also request a specific set of tests to be run. Perhaps a suffix /ci/cygwin, /ci/fedora, /ci/debian,fedora/TARGETS=pynormaliz/... (This idea needs to be fleshed out. See https://stackoverflow.com/questions/26382234/what-names-are-valid-git-tags)

Depends on #31210

CC: @dimpase @kliem @orlitzky @tobiasdiez

Component: porting

Keywords: ci, ContinuousIntegration

Issue created by migration from https://trac.sagemath.org/ticket/29535