Cross reference issue only repository from commits in code repository

Issue #15504 open
created an issue

S/w testers are not developers, instead of granting them access to code repo, we have created separate repo only to submit issues.

But we are not able to cross reference those issues from main code repo. For example following doesn't close the issue in 'issue-only-repo'.

git commit -m 'fixed issue-only-repo/issues#10 ...'

We are able to do that at github

It will be good to implement same here.