[MM-51076] Fix dropdown in modal for adding users in a group (#22642)

Co-authored-by: Mattermost Build <build@mattermost.com>

webapp/channels/src/components/create_user_groups_modal/__snapshots__/create_user_groups_modal.test.tsx.snap

@@ -65,7 +65,6 @@ exports[`component/create_user_groups_modal should match snapshot with back butt
   </ModalHeader>
   <ModalBody
     bsClass="modal-body"
-    className="overflow--visible"
     componentClass="div"
   >
     <div
@@ -184,7 +183,6 @@ exports[`component/create_user_groups_modal should match snapshot without back b
   </ModalHeader>
   <ModalBody
     bsClass="modal-body"
-    className="overflow--visible"
     componentClass="div"
   >
     <div

webapp/channels/src/components/create_user_groups_modal/create_user_groups_modal.scss

@@ -3,6 +3,10 @@
         margin-top: calc(50vh - 240px);
     }
 
+    .modal-body {
+        overflow: visible;
+    }
+
     .Input___error {
         &.group-error {
             position: absolute;

webapp/channels/src/components/create_user_groups_modal/create_user_groups_modal.tsx

@@ -213,9 +213,7 @@ export default class CreateUserGroupsModal extends React.PureComponent<Props, St
                     }
 
                 </Modal.Header>
-                <Modal.Body
-                    className='overflow--visible'
-                >
+                <Modal.Body>
                     <div className='user-groups-modal__content'>
                         <div className='group-name-input-wrapper'>
                             <Input