Upgrade anyio to 3.1 for all py versions

[mwakaba2]

Upgrade anyio to 3.1 for all supported python versions.

Fixes #505

[codecov-commenter]

Codecov Report

Merging #521 (a953e3b) into master (83a49c8) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #521      +/-   ##
==========================================
- Coverage   77.01%   76.97%   -0.04%     
==========================================
  Files         107      107              
  Lines        9511     9496      -15     
  Branches     1031     1031              
==========================================
- Hits         7325     7310      -15     
  Misses       1814     1814              
  Partials      372      372              

Impacted Files	Coverage Δ
...upyter_server/services/contents/filecheckpoints.py	62.94% <100.00%> (-0.65%)	⬇️
jupyter_server/services/contents/fileio.py	75.26% <100.00%> (-0.39%)	⬇️
jupyter_server/services/contents/filemanager.py	66.31% <100.00%> (-0.22%)	⬇️
...pyter_server/services/contents/largefilemanager.py	82.41% <100.00%> (-0.57%)	⬇️
jupyter_server/services/nbconvert/handlers.py	80.95% <100.00%> (-2.39%)	⬇️

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[blink1073]

Thank you!

[kevin-bates]

Thank you @mwakaba2 and @agronholm for taking care of this so quickly!