Add 3.12 to CI

[matmair]

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

[netlify]

✅ Deploy Preview for inventree-web-pui-preview canceled.

Name	Link
🔨 Latest commit	6456010
🔍 Latest deploy log	https://app.netlify.com/sites/inventree-web-pui-preview/deploys/6776d137434693000820ce07

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.17%. Comparing base (5eeb150) to head (6456010).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8592      +/-   ##
==========================================
+ Coverage   85.10%   85.17%   +0.07%     
==========================================
  Files        1178     1178              
  Lines       51748    51748              
  Branches     2091     2091              
==========================================
+ Hits        44040    44078      +38     
+ Misses       7178     7144      -34     
+ Partials      530      526       -4     

Flag	Coverage Δ
backend	86.90% <100.00%> (ø)
migrations	43.08% <0.00%> (-0.01%)	⬇️
pui	69.03% <ø> (+0.37%)	⬆️

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