This addresses a failure in the `py38-dev` tests
caused by markupsafe recently dropping Python 3.8 support.
Changed in this commit:
* Drop Python 3.8 support
* Update CI and tox testing
* Update docs references to Python 3.8
* Remove a Windows / Python 3.8 admonition in the docs
* Address type annotations
* Incorporate style fixes
Still to do:
* `src/flask/sessions.py` contains these comments:
> TODO generic when Python > 3.8
This TODO should now be unblocked.
* update pre-commit hook
* upgrade pip with venv
* update description and version
* show url in publish environment
* update versions
* update versions, separate typing job
* use dependabot grouped updates
ignore upload/download-artifact until slsa updates
* use sphinx.ext.extlinks instead of sphinx-issues
* update dev dependencies
* update editorconfig
* update gitignore
* update .readthedocs.yaml
* license is txt, readme is md
* update pyproject.toml
add typed classifier
add pyright config
simplify urls
* tox builds docs in place
* update min test py version
* add tox env to update all dev dependencies
* update issue and pr templates
* rename security docs page to not conflict with org policy file
* simplify matrix
