Merge branch 'mt/t4129-with-setgid-dir'

Some tests expect that "ls -l" output has either '-' or 'x' for
group executable bit, but setgid bit can be inherited from parent
directory and make these fields 'S' or 's' instead, causing test
failures.

* mt/t4129-with-setgid-dir:
  t4129: don't fail if setgid is set in the test directory