pipeline: fix missing `matrix.python-version` variable in "code-format" job
https://github.com/fphammerle/ical2vdir/commit/c62635bda1838ca9a103947ab4533d41e9ba74c5
https://github.com/fphammerle/python-manchester-code/commit/5c1a5ab7a4b96faecf02fe1eb266d367d70f37fd