build: match the node types package and node version

[zimeg]

Summary

This PR replaces #529 to prefer @types/node@20 to match our current supported Node version:

https://github.com/slackapi/slack-github-action/blob/3493f18217f6e55d55ff3ea694dec41304e53e97/.nvmrc

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 99.86%. Comparing base (3493f18) to head (39e7db0).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #531   +/-   ##
=======================================
  Coverage   99.86%   99.86%           
=======================================
  Files           7        7           
  Lines         722      722           
=======================================
  Hits          721      721           
  Misses          1        1           

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[zimeg]

@WilliamBergamin I appreciate the quick and kind review 🙏 ✨