Update tox and github actions.

[tim-schilling]

• Test with python 3.10
• Switch selenium test to py3.9 and django 3.2
• Use latest versions of mariadb and postgresql in CI

[codecov]

Codecov Report

Merging #1500 (e085001) into main (e20ac73) will increase coverage by 0.58%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1500      +/-   ##
==========================================
+ Coverage   85.73%   86.31%   +0.58%     
==========================================
  Files          35       35              
  Lines        1893     1893              
  Branches      273      276       +3     
==========================================
+ Hits         1623     1634      +11     
+ Misses        190      183       -7     
+ Partials       80       76       -4     

Impacted Files	Coverage Δ
debug_toolbar/middleware.py	96.66% <0.00%> (+1.66%)	⬆️
debug_toolbar/panels/headers.py	100.00% <0.00%> (+4.54%)	⬆️
debug_toolbar/panels/templates/views.py	67.44% <0.00%> (+4.65%)	⬆️
debug_toolbar/panels/history/panel.py	96.15% <0.00%> (+5.76%)	⬆️
debug_toolbar/views.py	100.00% <0.00%> (+25.00%)	⬆️

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