Merge branch 'en/dir-rename-tests'

More preliminary tests have been added to document desired outcome
of various "directory rename" situations.

* en/dir-rename-tests:
  t6423: more involved rules for renaming directories into each other
  t6423: update directory rename detection tests with new rule
  t6423: more involved directory rename test
  directory-rename-detection.txt: update references to regression tests