No missing user warning for public admin (#26611)

If airflow has been configured such that public role is admin, there's no need to add users, so we shouldn't warn if there are none.

(cherry picked from commit f01eed6)

airflow/www/fab_security/manager.py

@@ -820,7 +820,7 @@ def create_db(self):
         if self.auth_role_admin not in self.builtin_roles:
             self.add_role(self.auth_role_admin)
         self.add_role(self.auth_role_public)
-        if self.count_users() == 0:
+        if self.count_users() == 0 and self.auth_role_public != self.auth_role_admin:
             log.warning(LOGMSG_WAR_SEC_NO_USER)
 
     def reset_password(self, userid, password):