Impossible to unassign self from issue/MR in project where you're not a member

Summary

If you are assigned to an issue/MR on a project where you are not a member, you cannot unassign yourself (nor assign yourself).

Steps to reproduce

Create a public project in namespace A, create a fork by a user X not on the team of project A. Let X open an issue and make an MR.

1. Observe that X cannot assign herself to the issue or MR.
2. Observe that if A's team member assigns X to the issue or MR, she cannot unassign herself.

Expected behavior

A user should always be able to unassign themselves from an issue; potentially it might also make sense that the user would be able to self-assign the issue/MR they created even if it's not their project.

Actual behavior

Neither is possible.