Fix pre-commit / ruff errors

[dekkers]

I saw that the repository wasn't clean with regards to pre-commit / ruff. This PR fixes all the ruff errors.

I decided to silence the PTH123 error because Django returns strings and it doesn't make a lot of sense to me to convert the string to a Path object for a single open call just to make ruff happy.

It might also be a good idea to add https://pre-commit.ci/ to the repository to have pre-commit run in CI.

[semanticdiff-com]

Review changes with SemanticDiff.

Analyzed 4 of 4 files.

Overall, the semantic diff is 50% smaller than the GitHub diff.

2 files do not contain logic changes.

	Filename	Status
✔️	django_weasyprint/__init__.py	38.7% smaller
✔️	django_weasyprint/tests/__init__.py	No logic changes found
✔️	django_weasyprint/utils.py	12.5% smaller
✔️	django_weasyprint/views.py	No logic changes found