Improve text in MR widget when pipeline fails

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Follow up from #291168 (closed) where we changed the failure message.

As mentioned in Slack, I thought the new text was slightly confusing. Specifically, the first part: The pipeline for this merge request did not complete.

This kind of implies that the pipeline did not finish so it is confusing when the pipeline finished but failed which I think is actually the more common case compared to cancelled ones.

Some suggestions:

• The pipeline for this merge request did not complete successfully.
• The pipeline for this merge request did not succeed.
• The pipeline for this merge request was not successful.