Otherwise, the path "src/c-stdaux/src/docs/conf.py" matches for
formatting. But this file is imported via git-subtree, we don't
want to format it.
Filter out such paths.
This is more for completeness, to go along "nm-code-format.sh"
script.
Usually it's very simple to run black directly (you may still do that).
However, black by default only reformats files with ".py" extension.
So to get all our python files, you'd need to know and explicitly
select them... or use this script.
Also, `black .` scans the entire source tree, and is rather slow.
This script knows which files to select and is thus faster.
