[Fleet] Fix missing await in test making test flaky

[criamico]

Closes #150607

Summary

Flaky test was re-enabled last month but was failing again. An "await" was missing and was likely causing the flakiness.

Checklist

• Unit or functional tests were updated or added to match the most common scenarios

[apmmachine]

🤖 GitHub comments

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Just comment with:

• /oblt-deploy : Deploy a Kibana instance using the Observability test environments.
• run elasticsearch-ci/docs : Re-trigger the docs validation. (use unformatted text in the comment!)

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[criamico]

The flakiness in this run was due to some other test in FTR. I'm re running before merging just to be sure.

[criamico]

@elasticmachine merge upstream

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 8474037

Metrics [docs]

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	19	21	+2
securitySolution	398	401	+3
total			+5

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	20	22	+2
securitySolution	478	481	+3
total			+5

History

• 💛 Build #124851 was flaky 33bfe8e

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream