Removes empty alert from Insights page

What does this MR do and why?

Removes empty alert from Insights page after typo introduced in !130534 (diffs) and adds test coverage.

Screenshots or screen recordings

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Make sure you have a GitLab Ultimate license
2. Visit http://{LOCAL_INSTANCE}/groups/{GROUP_PATH}/-/insights or http://{LOCAL_INSTANCE}/{GROUP_PATH}/{PROJECT_PATH}/insights
3. Verify that the empty alert no longer appears

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.