chore: release slack-cli v4.2.1

[slack-cli-releaser]

Summary

Release v4.2.1.

Testing

• Confirm unit tests and E2E tests are passing on the branch.
• Confirm unit tests and E2E tests are passing on this PR.
• Confirm the dev-build includes all commits since last release.
• Review open issues or PRs on the "Next Release" milestone.
• Confirm the new version matches the expected next version.

Reviewers

After merging, create a GitHub Release to tag the new version.

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 71.67%. Comparing base (711bfee) to head (213e9dc).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #579      +/-   ##
==========================================
+ Coverage   71.66%   71.67%   +0.01%     
==========================================
  Files         226      226              
  Lines       19148    19148              
==========================================
+ Hits        13723    13725       +2     
- Misses       4216     4218       +2     
+ Partials     1209     1205       -4     

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