chore(release): version 3.40.0

[zimeg]

Summary

This PR releases the thinking steps efforts of #1824! 🤖

🔗 https://github.com/slackapi/python-slack-sdk/milestone/115

Category

• slack_sdk.web.WebClient (sync/async) (Web API client)
• slack_sdk.models (UI component builders)
• /docs (Documents)
• 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]

@lukegalbraithrussell Your review is so appreciated in these releases 🪬 ✨

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.96%. Comparing base (af6a7bb) to head (a3f405f).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@ Coverage Diff @@## main #1831 +/- ##
=======================================
Coverage 83.96% 83.96% =======================================
Files 116 116 Lines 13221 13221 =======================================
Hits 11101 11101 Misses 2120 2120 

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