Summary

A username that has an underscore or dash as either first, second or third character, doesn't show up as suggested reviewer in a PR

Steps to Reproduce

1. Create a user with username T-123
2. Give them access to a repo of yours
3. Create a PR in this repo
4. In the 'Reviewers' field of the PR, type 'T-'

Expected Results

The user T-123 should show up as suggested user

Actual Results

User 'T-123' is not suggested

Workaround

If the underscore or dash is the 1st character, copy-pasting the username in the Reviewer field will work.