ci: include the slack health score as part of ci tests

[zimeg]

Summary

This PR adds the 🏥 slackapi/slack-health-score to this action as part of regular check ups!

Hopes to fix strangeness that happens when adding this action another PR. I'm hoping this fixes missing commits, but am unsure if this is a real fix 😳

Notes

Please forgive the misuse of a diff but these are the errors shown in the other run:

> Run slackapi/slack-health-score@v0.1.1
    with:
      codecov_token: ***
      github_token: ***
      extension: js
    env:
      EVENT_URL: https://github.com/slackapi/slack-github-action/pull/333
  Using SHA: 7c719bb2a1a67ec8972d7edd09a24c26856f306f
  Pinging codecov API for coverage data...
- Error: Failed to retrieve codecov commits
- Error: FetchError: Unauthorized
- Warning: Directories to be included not specified
- Error: Error: spawnSync /bin/sh ENOBUFS
- Error: child_process execSync failed to execute
  {
    "comments": [],
    "coverageMisses": 0
  }
  Using SHA: 7c719bb2a1a67ec8972d7edd09a24c26856f306f
  -0

More notes

• Formatting of the main.yml is left to another PR or future change - hoping to keep this diff small ✨

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 97.91%. Comparing base (9bcc222) to head (4bac3f3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #346   +/-   ##
=======================================
  Coverage   97.91%   97.91%           
=======================================
  Files           2        2           
  Lines          96       96           
=======================================
  Hits           94       94           
  Misses          2        2           

☔ View full report in Codecov by Sentry.
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[zimeg]

@filmaj 🙏 Thanks for such speed in this review! I'm excited to see what'll happen on merge to main with a pull_request_target 😳

Let's find out! 🚀

[zimeg]

🤔 Hmmm no immediate results, but it's also true that the commit on main is the first with the health score. Perchance a run with the next commit changes things? I'll be keeping close watch on this 👁️