CI: Visibly print trailing whitespace when static checks fail

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.

.github/workflows/static_checks.yml

@@ -22,7 +22,8 @@ jobs:
           sudo apt-get install -qq dos2unix clang-format-15 libxml2-utils python3-pip moreutils
           sudo update-alternatives --remove-all clang-format || true
           sudo update-alternatives --install /usr/bin/clang-format clang-format /usr/bin/clang-format-15 100
-          sudo pip3 install black==22.3.0 pygments pytest==7.1.2 mypy==0.971
+          sudo pip3 install black==22.3.0 pytest==7.1.2 mypy==0.971
+          git config diff.wsErrorHighlight all
 
       - name: File formatting checks (file_format.sh)
         run: |