CI workflow: use checkout v3

[scpeters]

🦟 Bug fix

Part of gazebo-tooling/release-tools#862.

Summary

Version v2 of the actions/checkout workflow is deprecated, so switch to v3.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #334 (b342a15) into ign-fuel-tools4 (eb6c357) will not change coverage.
The diff coverage is n/a.

❗ Current head b342a15 differs from pull request most recent head 12ebe88. Consider uploading reports for the commit 12ebe88 to get more accurate results

@@               Coverage Diff                @@
##           ign-fuel-tools4     #334   +/-   ##
================================================
  Coverage            77.66%   77.66%           
================================================
  Files                   19       19           
  Lines                 2740     2740           
================================================
  Hits                  2128     2128           
  Misses                 612      612           

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