Resolve "Error getting performance bar results for <UUID>"

What does this MR do?

Two commits:

1. Ignore API requests from the performance bar (avoids the failure on https://gitlab.com/gitlab-org/gitlab-ce/issues?author_username=smcgivern).
2. Don't show a flash message when the performance bar fails for a request. If one doesn't show up, we can debug manually, but most of the time the flash message itself isn't helpful, and it can hide other banners.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the style guides

Closes #50801 (closed).