Change EXTRA_ARGS to be a multiValueArgs in GzFindPackage

[j-rivero]

🦟 Bug fix

Fixes #391

Summary

EXTRA_ARGS should really be a multiValueArgs as explained in the issue.

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.

[scpeters]

I've added a small test in #394, which I expect to fail in that draft PR, and if you cherry-pick it to this branch I expect it to pass. 🤞

[scpeters]

I've added a small test in #394, which I expect to fail in that draft PR, and if you cherry-pick it to this branch I expect it to pass. 🤞

a cmake warning was generated in CI for #394 as expected:

https://build.osrfoundation.org/job/gz_cmake-ci-pr_any-jammy-amd64/47/cmake/

please consider cherry-picking that test change into this branch

[j-rivero]

please consider cherry-picking that test change into this branch

Thanks so much for the test. Already cherry-picked.