Merge branch 'ps/t7527-fix-tap-output' into jch

A recent regression in t7527 that broke TAP output has been fixed,
some other test noise that also broke TAP output has been silenced,
and 'prove' is now configured to fail on invalid TAP output to
prevent future regressions.

* ps/t7527-fix-tap-output:
  t: let prove fail when parsing invalid TAP output
  t/lib-git-p4: silence output when killing p4d and its watchdog
  t/test-lib: silence EBUSY errors on Windows during test cleanup
  t7527: fix broken TAP output