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              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[mwbrooks]

✅ Thanks for adding Python 3.14 support!

🚀 Confirmed that 3.14 is run by the CI/CD