[Dev] Some assignments from the PR bot fail due to anti-spam protection

### Describe the bug, including details regarding any error messages, version, and platform.

If a user has not commented on an issue and does not have write access to the repository it is not possible to assign them. This is a GitHub spam protection that can not be circumvented. We should check for successful assignment in the PR bot and otherwise add a comment with instruction on how to self-assign the ticket.

### Component(s)

Developer Tools

Locate the PR bot's assignment handling from the Developer Tools implementation and inspect how assignment success or failure is reported. Reproduce the anti-spam failure if possible, then verify that failed assignments produce a comment explaining how the user can self-assign.

Written by the indexing model from the issue text.