Set GZ_IP=127.0.0.1 in gz cmd tests (backport #2884)

[mergify]

🦟 Bug fix

Fixes some tests using a cherry-pick from #2857

Summary

This cherry-picks 93f25a4 from #2857 to fix gz cmd test failures.

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.

---

This is an automatic backport of pull request #2884 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 3f40ef2 has failed:

On branch mergify/bp/gz-sim8/pr-2884
Your branch is up to date with 'origin/gz-sim8'.

You are currently cherry-picking commit 3f40ef29.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   src/cmd/CMakeLists.txt

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[scpeters]

easier to apply manually