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.

Follow-up to #488 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 #490 (09738cd) into ign-physics5 (4856580) will not change coverage.
The diff coverage is n/a.

❗ Current head 09738cd differs from pull request most recent head c65df42. Consider uploading reports for the commit c65df42 to get more accurate results

@@              Coverage Diff              @@
##           ign-physics5     #490   +/-   ##
=============================================
  Coverage         76.35%   76.35%           
=============================================
  Files               129      129           
  Lines              5810     5810           
=============================================
  Hits               4436     4436           
  Misses             1374     1374           

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