Add Python 3.11 in testing and refine uploading Codecov reports

[yuekui]

• Added Python 3.11 env in actions and tox, but since lxml has no wheels ready for MacOS and Windows, I just excluded them.
• Fixed the condition of uploading reports to Codecov.
• Removed some old Django versions since they did not officially support higher Python versions.

[codecov]

Codecov Report

Merging #683 (10a65cf) into main (56342be) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              main      #683   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines          290       290           
=========================================
  Hits           290       290           

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[jackton1]

Awesome 👏

[yuekui]

Thanks @jackton1 ! I think we should also update the required status checks in branch protection rules.