Lint on GitHub Actions (#196)

- Lint with pre-commit on GitHub Actions,
- Add some handy pre-hooks,
- Configure Ruff lint rules (https://github.com/astral-sh/ruff).

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Co-authored-by: Marc Wrobel <marc.wrobel@gmail.com>

src/sles.py

@@ -1,4 +1,3 @@
-import re
 from bs4 import BeautifulSoup
 from common import dates
 from common import endoflife