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.
It's too hard to get compatibility between GNU and BSD sed,
so let's just use perl oneliners.
And improve it to also remove trailing tabs, not just spaces.
