Nightly pre-release tests

[philkra]

• run nightly pre-release test on the release branch
• push status into Slack

Disable-check: force-changelog-file
Disable-check: approval-count

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.90%. Comparing base (59f50f2) to head (b7e22f9).
Report is 809 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7804      +/-   ##
==========================================
+ Coverage   80.06%   81.90%   +1.83%     
==========================================
  Files         190      247      +57     
  Lines       37181    45466    +8285     
  Branches     9450    11371    +1921     
==========================================
+ Hits        29770    37239    +7469     
- Misses       2997     3751     +754     
- Partials     4414     4476      +62     

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