[FIX] mail: always hide the dropzone when something is dropped

Before this commit, when an invalid element was dropped (e.g. dragging a
mention) the drop area freeze and make the UI unusable.

task-2373971

closes odoo/odoo#61792

X-original-commit: 629b54dc1249c77d1e30240c0b5a91e22a1ae110
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/mail/static/src/component_hooks/use_drag_visible_dropzone/use_drag_visible_dropzone.js

@@ -75,9 +75,7 @@ function useDragVisibleDropZone() {
      */
     function _onDropListener(ev) {
         dragCount = 0;
-        if (dropzoneRef.comp && !dropzoneRef.comp.contains(ev.target)) {
-            isVisible.value = false;
-        }
+        isVisible.value = false;
     }
 
     return isVisible;