fix #24429 (#24491)

lib/ansible/modules/system/user.py

@@ -2068,20 +2068,17 @@ class HPUX(User):
                     if self.append:
                         for g in groups:
                             if g in group_diff:
-                                if has_append:
-                                    cmd.append('-a')
                                 groups_need_mod = True
                                 break
                     else:
                         groups_need_mod = True
 
             if groups_need_mod:
-                if self.append and not has_append:
-                    cmd.append('-A')
-                    cmd.append(','.join(group_diff))
-                else:
-                    cmd.append('-G')
-                    cmd.append(','.join(groups))
+                cmd.append('-G')
+                new_groups = groups
+                if self.append:
+                    new_groups = groups | set(current_groups)
+                cmd.append(','.join(new_groups))
 
 
         if self.comment is not None and info[4] != self.comment: