Bot does not recognize GitHub usernames prefixed with `@`

Some users prefix their GitHub username with `@`, and the bot does not clean this character out from potential usernames when doing an Adobe Sign search.

Perhaps we could handle this on the bot end?

Start by locating the bot code that performs the Adobe Sign username search and check how potential GitHub usernames are extracted. The issue is done when usernames prefixed with `@` are recognized correctly during that search; no specific file or test is named in the issue.

Written by the indexing model from the issue text.