Ensure minimal nbconvert support jinja2 v2 & v3

[fcollonval]

Fix https://github.com/jupyter-server/jupyter_server/runs/5681044426?check_suite_focus=true where nbconvert 5.6.1 is used. But jinja2 3.1 was just release and drop some deprecated functions from v2. So requires at least nbconvert 6.2 that handle both jinja2 v2 and v3.

[fcollonval]

Xref #755

[codecov-commenter]

Codecov Report

Merging #756 (71500d5) into main (cd1b1b8) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #756      +/-   ##
==========================================
- Coverage   70.68%   70.64%   -0.04%     
==========================================
  Files          62       62              
  Lines        7620     7620              
  Branches     1218     1218              
==========================================
- Hits         5386     5383       -3     
- Misses       1860     1861       +1     
- Partials      374      376       +2     

Impacted Files	Coverage Δ
jupyter_server/base/zmqhandlers.py	52.91% <0.00%> (-4.24%)	⬇️
jupyter_server/services/kernels/kernelmanager.py	80.63% <0.00%> (-1.91%)	⬇️
jupyter_server/services/kernels/handlers.py	58.86% <0.00%> (-0.22%)	⬇️
jupyter_server/services/contents/manager.py	83.65% <0.00%> (+1.46%)	⬆️
jupyter_server/utils.py	62.20% <0.00%> (+2.87%)	⬆️

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[blink1073]

We're getting hit by pypa/setuptools#3200. I'm working on workarounds for releaser and server now.

[blink1073]

nbclient 0.5.0 depends on jupyter-client>=6.1.5, we need to bump that as well.

[Zsailer]

Thanks for tracking this down, @fcollonval and @blink1073. Looks good.

[blink1073]

Looks good.

Still working through the removal of implicit ipython_genutils in various packages. 😅

[blink1073]

All green except for the flaky windows test. Thanks @fcollonval!

[fcollonval]

Thanks @blink1073 for the continuous maintenance.