[BUG] oss.gg allows self assignment under PRs 

### Issue Summary

the  / assign command allows people to assign a PR to themselves

### Steps to Reproduce

try the / assign command in the comments under a PR


### Expected behavior

the command should only assign issues

### Other information

_No response_

### Screenshots

_No response_

### Desktop (please complete the following information)

```markdown
- OS:
- Node:
- npm:
```
