Update to Python 3.10 in the CI workflows

[jtpio]

Spotted while looking at the content of the workflows.

Normally it should be fine to switch to 3.10 final now.

[codecov-commenter]

Codecov Report

Merging #618 (61b2eeb) into master (e3eec2a) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #618      +/-   ##
==========================================
+ Coverage   77.58%   77.61%   +0.03%     
==========================================
  Files         110      110              
  Lines       10402    10402              
  Branches     1287     1287              
==========================================
+ Hits         8070     8074       +4     
+ Misses       1933     1930       -3     
+ Partials      399      398       -1     

Impacted Files	Coverage Δ
jupyter_server/services/kernels/handlers.py	62.40% <0.00%> (+1.00%)	⬆️

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[blink1073]

Thanks!