CI workflow: use checkout v3 in jammy

[scpeters]

🦟 Bug fix

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

Summary

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

Follow-up to #1225 that missed jammy when merged forward.

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 #1245 (5726937) into sdf12 (8d89537) will not change coverage.
The diff coverage is n/a.

❗ Current head 5726937 differs from pull request most recent head e2bbc6c. Consider uploading reports for the commit e2bbc6c to get more accurate results

@@           Coverage Diff           @@
##            sdf12    #1245   +/-   ##
=======================================
  Coverage   92.03%   92.03%           
=======================================
  Files          79       79           
  Lines       13090    13090           
=======================================
  Hits        12047    12047           
  Misses       1043     1043           

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[mjcarroll]

Windows failure is unrelated, I'm going to merge.