GitHub Actions seems to be hiding colored whitespace, and after lots of
attempts I couldn't find a way to work it around.
So instead I'm using a perl expression to replace trailing spaces with
`·` and tabs with `<TAB>` in the ANSI colored diff output. This ensure
that they're visible, and they are properly colored as expected too.
Follow-up to #55785.
In `black_format.sh`, the `--exclude` switch was wrongly used. It's a misnomer
that only excludes _untracked_ files, arcane pathspec patterns should instead
be used to exclude _tracked_ files.
Using this newfound knowledge, we can also simplify the other scripts.
