feat: add support for python 3.14

[WilliamBergamin]

Summary

These changes ensures the project officially support python 3.14

Testing

The CI will run the tests against python 3.14

Category

• slack_bolt.App and/or its core components
• slack_bolt.async_app.AsyncApp and/or its core components
• Adapters in slack_bolt.adapter
• Document pages under /docs
• Others

Requirements

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you are agreeing to those rules.

• 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 ./scripts/install_all_and_run_tests.sh after making the changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.54%. Comparing base (2086c7a) to head (25fd19e).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@ Coverage Diff @@## main #1397 +/- ##
==========================================
- Coverage 91.05% 90.54% -0.51% 
==========================================
Files 222 222 Lines 7534 7129 -405 ==========================================
- Hits 6860 6455 -405 
Misses 674 674 

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[mwbrooks]

✅ Thanks for adding Python 3.14 support!

🚀 Confirmed that 3.14 is run by the CI/CD