What steps will reproduce the problem?
(1) Create a CL with modifications under tools/grit
(2) Run git cl presubmit

What is the expected result?

Presubmit tests run, i.e. the same thing should occur as:

$ cd tools/grit
$ python -m grit.test_suite_all

OR:

$ cd tools/grit/grit
$ python -m test_suite_all

What happens instead?

Presubmit tests fail, because failing in starting tests.

grit.test_suite_all (0.08s) failed
/path/to/python: No module named test_suite_all

This is because what is executed corresponds to the following:

$ cd tools/grit
$ python -m test_suite_all

This is an regression in depot_tools.
The first bad CL was:
https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/973691