Error 500 when promoting issue into an epic

Trying to promote an issue into an epic is throwing a 500 error.

How to reproduce

Go to #363801 (closed) and try to promote it to an epic using quick action or the button at the top navigation bar.

The promotion fails with an error message. Full error trace at https://gitlab.com/gitlab-org/gitlab/blob/83cd6733acd704a8dfab64c5b2bc67238805ef7d/lib/gitlab/issuable/clone/attributes_rewriter.rb.

A query to fetch labels is timing out. Could be related to a recent change at https://gitlab.com/gitlab-org/gitlab/blob/83cd6733acd704a8dfab64c5b2bc67238805ef7d/lib/gitlab/issuable/clone/attributes_rewriter.rb.