Closes GH-620.
Closes GH-633.
Closes GH-621.
We add a copy of the latest run-tests.php from the PHP-8.0 branch, and tests for the `UserNotes\Sorter` with full code coverage. We also run tests on GitHub Actions. Co-authored-by: Andreas Möller <am@localheinz.com> Closes GH-606.
Closes GH-554.