Fix python install directory

[azeey]

🦟 Bug fix

Summary

The gz directory was missing from the install path. The contents of the deb file before this PR is

/.
/usr
/usr/lib
/usr/lib/python3
/usr/lib/python3/dist-packages
/usr/lib/python3/dist-packages/transport13
/usr/lib/python3/dist-packages/transport13/__init__.py
/usr/lib/python3/dist-packages/transport13/_transport.cpython-310-x86_64-linux-gnu.so
/usr/share
/usr/share/doc
/usr/share/doc/python3-gz-transport13
/usr/share/doc/python3-gz-transport13/changelog.Debian.gz
/usr/share/doc/python3-gz-transport13/copyright

It should be /usr/lib/python3/dist-packages/gz/transport13/

Needed by https://github.com/gazebosim/gz-sim/pull/2081

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.