Merge branch 'en/test-cleanup'

Test cleanup. * en/test-cleanup: t6020: new test with interleaved lexicographic ordering of directories t6022, t6046: test expected behavior instead of testing a proxy for it t3035: prefer test_must_fail to bash negation for git commands t6020, t6022, t6035: update merge tests to use test helper functions t602[1236], t6034: modernize test formatting