fix typos discovered by codespell

[cclauss]

Fix typos discovered by codespell - https://pypi.org/project/codespell

% codespell --ignore-words-list=te

./docs/appcontext.rst:122: requet ==> request
./docs/quickstart.rst:465: interanlly ==> internally
./docs/templating.rst:186: avaialble ==> available

% codespell -ignore-words-list=te --write-changes

[davidism]

See our contributing guide about docs https://palletsprojects.com/contributing/docs, in particular

If you are fixing or improving existing docs, or writing about existing features, you want to branch off of the stable branch, as well as target the stable branch in the PR.

[cclauss]

Unfortunately, the three typos above are not on the stable branch, so let's get codespell in place to catch future typos.

• pre-commit: Add codespell #5844