Add 3.12 to CI

[matmair]

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

[netlify]

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🔨 Latest commit	2d9377f
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Lighthouse	1 paths audited Performance: 99 (🔴 down 1 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 84.67%. Comparing base (7a3ceb9) to head (2d9377f).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8592      +/-   ##
==========================================
+ Coverage   84.60%   84.67%   +0.06%     
==========================================
  Files        1188     1189       +1     
  Lines       54270    54285      +15     
  Branches     2050     2054       +4     
==========================================
+ Hits        45914    45964      +50     
+ Misses       7849     7802      -47     
- Partials      507      519      +12     

Flag	Coverage Δ
backend	86.05% <ø> (+<0.01%)	⬆️
migrations	42.62% <ø> (-0.01%)	⬇️
pui	69.31% <ø> (+0.39%)	⬆️

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