Speed up rabbit managements tests (backport #11496)

[mergify]

main: gmake -C deps/rabbitmq_management tests 16.75s user 12.51s system 3% cpu 13:12.46 total

this PR: gmake -C deps/rabbitmq_management tests 15.21s user 10.73s system 8% cpu 4:48.54 total

---

This is an automatic backport of pull request #11496 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of a9ac9c4 has failed:

On branch mergify/bp/v3.13.x/pr-11496
Your branch is ahead of 'origin/v3.13.x' by 2 commits.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit a9ac9c46cf.
  (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:   deps/rabbitmq_management/test/rabbit_mgmt_http_SUITE.erl

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

Cherry-pick of de821c3 has failed:

On branch mergify/bp/v3.13.x/pr-11496
Your branch is ahead of 'origin/v3.13.x' by 4 commits.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit de821c33f8.
  (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)

Changes to be committed:
	modified:   deps/rabbitmq_ct_helpers/src/rabbit_mgmt_test_util.erl
	modified:   deps/rabbitmq_management/test/rabbit_mgmt_only_http_SUITE.erl
	modified:   deps/rabbitmq_management_agent/src/rabbit_mgmt_metrics_collector.erl

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   deps/rabbitmq_management/test/rabbit_mgmt_test_db_SUITE.erl

Cherry-pick of 5103309 has failed:

On branch mergify/bp/v3.13.x/pr-11496
Your branch is ahead of 'origin/v3.13.x' by 5 commits.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit 51033093fd.
  (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:   deps/rabbitmq_management/test/rabbit_mgmt_only_http_SUITE.erl

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