chore: release slack-cli v3.12.0

[zimeg]

Summary

This PR tags the latest changes on main as 3.12.0 👾

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.

[mwbrooks]

🚀 Nice, loving seeing the docs updated in these release PRs!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.61%. Comparing base (252bf7f) to head (30f5df9).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #319      +/-   ##
==========================================
- Coverage   64.63%   64.61%   -0.02%     
==========================================
  Files         212      212              
  Lines       17755    17755              
==========================================
- Hits        11476    11473       -3     
- Misses       5205     5206       +1     
- Partials     1074     1076       +2     

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