ci: enable doxygen checks

[scpeters]

🦟 Bug fix

Part of gazebo-tooling/release-tools#1222.

Summary

Try enabling doxygen checks in GitHub workflow since #1409 has been resolved.

The following errors will be fixed by the following PRs:

2025-06-09T18:39:59.7739484Z error: Tag file '/usr/share/gz/gz-plugin/gz-plugin.tag.xml' does not exist or is not a file. Skipping it...
2025-06-09T18:39:59.7740926Z error: Tag file '/usr/share/gz/gz-sensors/gz-sensors.tag.xml' does not exist or is not a file. Skipping it...

• Install doxygen tag.xml to unversioned folder gazebo-release/gz-plugin4-release#3
• Install doxygen tag.xml to unversioned folder gazebo-release/gz-sensors10-release#5

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
• Was GenAI used to generate this PR? If so, make sure to add "Generated-by" to your commits. (See this policy for more info.)

Generated-by: Remove this if GenAI was not used.

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