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

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