Add 3.12 to CI

[matmair]

This PR (re) adds 3.12 to the CI in preparation for #8582

[netlify]

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Lighthouse	1 paths audited Performance: 99 (no change from production) Accessibility: 86 (no change from production) Best Practices: 100 (no change from production) SEO: 78 (no change from production) PWA: - View the detailed breakdown and full score reports

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.30%. Comparing base (933330f) to head (4282971).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8592      +/-   ##
==========================================
+ Coverage   85.24%   85.30%   +0.06%     
==========================================
  Files        1175     1175              
  Lines       52444    52443       -1     
  Branches     2089     2089              
==========================================
+ Hits        44704    44735      +31     
+ Misses       7241     7203      -38     
- Partials      499      505       +6     

Flag	Coverage Δ
migrations	43.18% <ø> (+<0.01%)	⬆️

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