Use GITHUB_OUTPUT envvar instead of set-output command as the latter is deprecated

[arunsathiya]

Summary

save-state and set-output commands used in GitHub Actions are deprecated and GitHub recommends using environment files.

This PR updates the usage of set-output to $GITHUB_OUTPUT

Instructions for envvar usage from GitHub docs:

https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#setting-an-output-parameter

Testing

• I think the next publish action should successfully go through?

Special notes

I have scanned all repositories owned by slackapi (thanks to gh-clone-org extension from this issue) and there is only one instance of usage.

It's set-output on the npm-publish workflow for deno-slack-sdk repository.

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 ran deno task test after making the changes.

[arunsathiya]

This is the only change being proposed in this PR. The rest of the changes are formatting corrections made by my IDE.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ca8e418) 98.07% compared to head (34feb7c) 98.07%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #261   +/-   ##
=======================================
  Coverage   98.07%   98.07%           
=======================================
  Files          58       58           
  Lines        2280     2280           
  Branches      137      137           
=======================================
  Hits         2236     2236           
  Misses         42       42           
  Partials        2        2           

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

[filmaj]

Thanks!