MR reference in commit-pipelines page never loads

Summary

When viewing the page that displays all pipelines associated with a particular commit, the MR reference spins and spins but never loads the related MR nor displays "No related MRs".

This comes after the recent addition of gitlab-ce!13713.

Steps to reproduce

Open a commit-pipelines URL of the form www.gitlab.com/<group>/<project>/commit/<hash>/pipelines, and see the related MR spinner.

Example

See any commit here in gitlab-ce project, such as:

• commit/76bfc161 page resolves the related MR just fine. [expected behavior]
• commit/76bfc161/pipelines page never resolves the related MR. [current behavior]

Related: gitlab-ce#2383