[8.19] (backport #11539) Ensure we don't report output status in tests where it's irrelevant

[mergify]

What does this PR do?

In some tests, we use a nonexistent ES host to avoid needing to use a remote. Output health reporting actually works for beats receivers, so this can lead to flakiness due to components reporting a degraded state. Disable the status reporting where it's irrelevant to the test.

This takes care of remaining tests that I missed in #11257.

Why is it important?

Tests shouldn't randomly fail because the output correctly reports a degraded status. Example failure: https://buildkite.com/elastic/elastic-agent/builds/31319/steps/table?jid=019adfc5-7d8c-4a2a-a437-5cb33fe32bcb.

Checklist

• I have read and understood the pull request guidelines of this project.
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have made corresponding change to the default configuration files
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added an entry in ./changelog/fragments using the changelog tool
• [ ] I have added an integration test or an E2E test

---

This is an automatic backport of pull request #11539 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of b8a142f has failed:

On branch mergify/bp/8.19/pr-11539
Your branch is up to date with 'origin/8.19'.

You are currently cherry-picking commit b8a142f54.
  (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:   testing/integration/ess/diagnostics_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   testing/integration/ess/beat_receivers_test.go

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

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: b7febde

Failed CI Steps

• x86_64:sudo: default - platform-ingest-elastic-agent-debian-13-1762801856

cc @swiatekm