chore: added logic to accomendate the dual use of add_member

app/models/team.rb

@@ -78,7 +78,7 @@ def full?
 
   # Add member to the team, changed to hash by E1776
   def add_member(user, _assignment_id = nil)
-    username = user?(user) ? user.username : user.name
+    username = user.method_defined? :username ? user.username : user.name
     raise "The user #{username} is already a member of the team #{name}" if user?(user)
 
     can_add_member = false