Clean up CI

[blink1073]

• Allow tests to be flaky by using --lf
• Force the WinPTY backend for terminals
• Increase test timeouts
• Fix nbclassic downstream test - depends on Clean up handling of downstream tests jupyterlab/maintainer-tools#62

[codecov-commenter]

Codecov Report

Merging #723 (3e9d458) into main (fb25932) will decrease coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #723      +/-   ##
==========================================
- Coverage   70.94%   70.87%   -0.07%     
==========================================
  Files          62       62              
  Lines        7502     7515      +13     
  Branches     1190     1190              
==========================================
+ Hits         5322     5326       +4     
- Misses       1823     1834      +11     
+ Partials      357      355       -2     

Impacted Files	Coverage Δ
jupyter_server/services/kernels/kernelmanager.py	80.69% <0.00%> (-1.85%)	⬇️
jupyter_server/services/contents/filemanager.py	70.72% <0.00%> (+0.10%)	⬆️

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[blink1073]

Drat, it looks like the nbclassic failure is legit.

[blink1073]

I opened jupyter/nbclassic#91, we'll need a release of that to be sure. I think the test timeouts are going to be blocked on jupyter/jupyter_client#751, so I don't think we should block this PR on that.

[blink1073]

Let's merge and iterate since this is already an improvement.