[BUG] Bot can @-mention random GitHub users if commit authors can't be matched to a user

[iliana]

Describe the bug
When a commit is pushed and a commit author can't be resolved to a GitHub user, the comment this action posts to the issue uses the author name prepended with @. This can cause a notification to a completely random user.

To Reproduce
git commit --author="ghost <ghost@example.invalid>"

Expected behavior
Please don't use an @ if you already know the text following it isn't a GitHub username.

Screenshots

(via edit history of this comment)

[W0lfbane]

Hello, may I please ask you to use this image for your bug evidence? I have blurred out my last name.