Alert on MRs `Something went wrong on our end while loading the code quality diff`

Overview

The following red banner is appearing on MRs:

Internal thread: https://gitlab.slack.com/archives/CETG54GQ0/p1623239652216500

This banner used to be blank, which was fixed by !63230 (merged)

I was able to reproduce this by switching to and from an MR tab. Whenever I switched focus to the MR tab, the banner appeared.

Current Status

The feature flag to disable this feature was flipped so it is off by default on Gitlab.com as of 2021-06-21 and will be picked into 14.0.1.

Proposal

1. This should be changed to fail silently as any alert just interferes with the Code Review workflow
2. This also matches with case #3 (closed) in issue with #327751 (closed) so not displaying anything until that processing is done would also fix this.