sysusers: check if requested group name matches user name in queue

sysusers: check if requested group name matches user name in queue

When creating a user, check if the requested group name matches a user
name in the queue. If that matched user name is also going to be a group
name, then use it for the new user too. In other words, allow the
following:

 u foo -
 u bar -:foo

when both foo and bar are new users.

Fixes #33547

(cherry picked from commit 18a8f03e5160ca3828d327d9bbd1b32f26d792a3)