Remove highlight from reactions

This explicitly sets `color` for the reactions row to ensure it's always the fg
colour, even if the event is highlighted.

Fixes https://github.com/vector-im/riot-web/issues/9697

res/css/views/messages/_ReactionsRow.scss

@@ -16,4 +16,5 @@ limitations under the License.
 
 .mx_ReactionsRow {
     margin: 6px 0;
+    color: $primary-fg-color;
 }