ci: post regression notifications if scheduled tests do not succeed

[zimeg]

Summary

This PR matches the changes of slackapi/bolt-python#1376 to send regression notifications if scheduled tests do not succeed instead of just during failures. Fixes an issue where test timeout do not post a message.

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.37%. Comparing base (f8c3987) to head (bd22227).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2667   +/-   ##
=======================================
  Coverage   93.37%   93.37%           
=======================================
  Files          37       37           
  Lines        7581     7581           
  Branches      667      667           
=======================================
  Hits         7079     7079           
  Misses        497      497           
  Partials        5        5           

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[WilliamBergamin]

Nice 💯

[zimeg]

@WilliamBergamin Woot! We should bring these scheduled checks to other projects soon, per your great suggestion 🤖 ✨