[LINTER] Fix the python format string when dealing with arrays

Summary:
Thanks to Mark for finding the bug.

The lint-python-format.py linter failed the transformation when the
qualifier was an array. This diff adds the case management and update
the tests accordingly.

Test Plan:
Should return nothing:

./test/lint/lint-python-format.py

arc lint --everything

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D3517