[PR #8304/88c80c14 backport][3.10] Check for backports in CI

[patchback]

This is a backport of PR #8304 as merged into master (88c80c1).

Add a check for backport labels due to several PRs having missed backports by mistake.
We have a backport:skip label if we explicitly don't want to backport a PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.48%. Comparing base (767c413) to head (e53a9b3).

Additional details and impacted files

@@            Coverage Diff             @@
##             3.10    #8306      +/-   ##
==========================================
+ Coverage   97.42%   97.48%   +0.06%     
==========================================
  Files         108      108              
  Lines       33268    33268              
  Branches     3973     3973              
==========================================
+ Hits        32410    32432      +22     
+ Misses        645      627      -18     
+ Partials      213      209       -4     

Flag	Coverage Δ
CI-GHA	97.39% <ø> (+0.05%)	⬆️
OS-Linux	97.06% <ø> (+0.05%)	⬆️
OS-Windows	94.70% <ø> (+0.06%)	⬆️
OS-macOS	96.78% <ø> (+0.16%)	⬆️
Py-3.10.11	94.52% <ø> (ø)
Py-3.10.14	96.86% <ø> (+0.03%)	⬆️
Py-3.11.8	97.05% <ø> (+<0.01%)	⬆️
Py-3.12.2	97.16% <ø> (ø)
Py-3.8.10	94.45% <ø> (ø)
Py-3.8.18	96.70% <ø> (ø)
Py-3.9.13	94.51% <ø> (?)
Py-3.9.19	96.83% <ø> (+0.02%)	⬆️
Py-pypy7.3.15	96.36% <ø> (?)
VM-macos	96.78% <ø> (+0.16%)	⬆️
VM-ubuntu	97.06% <ø> (+0.05%)	⬆️
VM-windows	94.70% <ø> (+0.06%)	⬆️

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