@username doesn't work if username contains a hyphen

[robatino]

I attempted to reply in Bodhi to user "roman-averin" using the @ sign, but it only recognizes the part of the username before the hyphen. For example, see https://bodhi.fedoraproject.org/updates/FEDORA-2023-ee241dcf80 . I saw no way to make it work so just removed my attempt. If there is a way to do it, it needs to be documented. The link to Fedora-Flavored Markdown says nothing.

[mattiaverga]

Hopefully, it just needs to better define the regex at
MENTION_RE = r'(?<!\S)(@\w+)'