Fix drag-and-drop to Chromium

Summary: BUG: 369404

Test Plan:
Tested in KDE Neon:
- Drag-and-drop to Chromium window works now
- Drag-and-drop to Firefox window still works
- Drag-and-drop to the Desktop still works
- Drag-and-drop to Dolphin window still works
- Drag-and-drop to GIMP window still works
- Drag-and-drop to Gwenview window still works

Reviewers: #spectacle, sebas, rkflx

Reviewed By: rkflx

Subscribers: rkflx

Differential Revision: https://phabricator.kde.org/D10427