Merge branch 'bl/t7412-use-test-path-helpers' into jch

The test script 't7412' that tests 'git submodule absorbgitdirs' has
been modernized to use test_path_is_file(), test_path_is_dir(), and
test_path_is_missing() helper functions instead of raw 'test -[fde]'
commands.

* bl/t7412-use-test-path-helpers:
  submodule absorbgitdirs tests: use test_* helper functions