Update skunk workflows

[JuanVqz]

• [x] Add an entry to CHANGELOG.md that links to this PR under the "main (unreleased)" heading.

Description:

When working on https://github.com/fastruby/skunk/pull/103 I saw the CI was broken, so, this is fixing it.

I will abide by the code of conduct.

[codecov[bot]]

Codecov Report

Merging #104 (d6f01e4) into main (6a601a5) will not change coverage. The diff coverage is n/a.

:exclamation: Current head d6f01e4 differs from pull request most recent head 50c8215. Consider uploading reports for the commit 50c8215 to get more accurate results

@@           Coverage Diff           @@
##             main     #104   +/-   ##
=======================================
  Coverage   98.27%   98.27%           
=======================================
  Files          25       25           
  Lines         465      465           
=======================================
  Hits          457      457           
  Misses          8        8           

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[JuanVqz]

Just for the record, this compatibility page helped me to know what bundler's version corresponds to which Ruby.