Support gz-cmake without major version

[scpeters]

🦟 Bug fix

Needed for jetty bumps: gazebosim/gz-plugin#175, gazebosim/sdformat#1561

Summary

Support for gz-cmake5 was added in #158, but the major version has been removed from the package name, so now support gz-cmake instead.

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.