CI/DOC: Unpin jinja2
- [x] closes #46514 (Replace xxxx with the Github issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Should be closed by https://github.com/jupyter/nbconvert/pull/1737; we'll see if CI agrees. Also specifies `nbconvert>=6.4.5`; this is the most recent version of nbconvert but because this is only for dev I think it's okay.
@meeseeksdev backport 1.4.x thanks @rhshadrach  Something went wrong ... Please have a look at my logs.