Update nbconvert

[zaqqwerty]

Tutorial tests in CI are starting to show the following error:

ImportError: cannot import name 'contextfilter' from 'jinja2' (/opt/hostedtoolcache/Python/3.8.12/x64/lib/python3.8/site-packages/jinja2/__init__.py)
Tutorials failed to run to completion:
{}

We currently use version 5.6.1, but going to the latest version seems to fix the issue for others.