fix(explore): Dataset icon remains constant when dragging. (#12761)

* fix: constant icon size

* clean up

superset-frontend/src/explore/components/controls/DatasourceControl.jsx

@@ -89,6 +89,7 @@ const Styles = styled.div`
   }
   .dataset-svg {
     margin-right: ${({ theme }) => 2 * theme.gridUnit}px;
+    flex: none;
   }
 `;