ci: send regression notifications if prior jobs do not succeed on schedule

[zimeg]

Summary

This PR adds scheduled regression tests to CI for earlier alerts if dependencies cause builds to break.

Testing

Following commits will be used as a proof of concept!

Category

• tests/integration_tests (Automated tests for this library)

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.
• I've run python3 -m venv .venv && source .venv/bin/activate && ./scripts/run_validation.sh after making the changes.

[zimeg]

🗣️ We might be failing a test already! But the ordering of these jobs seems alright to me:

🔗 https://github.com/slackapi/python-slack-sdk/pull/1768/checks

[zimeg]

📝 I notice a handful of required checks don't match the updated steps - if these changes seem alright we can perhaps update what's required to match?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.12%. Comparing base (344e0c5) to head (db74dec).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@ Coverage Diff @@## main #1768 +/- ##
=======================================
Coverage 85.12% 85.12% =======================================
Files 115 115 Lines 13068 13068 =======================================
Hits 11124 11124 Misses 1944 1944 

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[mwbrooks]

🗣️ We might be failing a test already! But the ordering of these jobs seems alright to me:

Any idea why these are failing? The PR looks straight forward, but is it introducing these failures?

[zimeg]

Any idea why these are failing? The PR looks straight forward, but is it introducing these failures?

@mwbrooks I had to investigate this and I believe the changes of #1769 might be promising in resolving this! Let's find out soon 👁️‍🗨️

[WilliamBergamin]

Nice 💯 I like this improvement to our CI

[WilliamBergamin]

Praise 🙏

[WilliamBergamin]

The branch rules were updated to match the new Jobs names 💯 we will need to merge this PR before merging other changes

[zimeg]

@mwbrooks@WilliamBergamin Thanks both for the reviews and help in improvements to these checks! 🧪 ✨

I'll merge this once tests are passing to unblock other jobs - will monitor these scheduled runs later ⏳

[zimeg]

⏳ Nice! This seems to've started as we hope: https://github.com/slackapi/python-slack-sdk/actions/runs/18668441391