Enable MergeableSelector in scss-lint (for !14062)

app/assets/stylesheets/pages/projects.scss

@@ -88,7 +88,8 @@
   transition: background 2s ease-out;
   &:disabled {
-    opacity: 0.75;
+    opacity: 0.5;
+    pointer-events: none;
   }
   .highlight-changes & {
@@ -1160,13 +1161,6 @@ pre.light-well {
   }
 }
-.project-repo-select {
-  &.disabled {
-    opacity: 0.5;
-    pointer-events: none;
-  }
-}
-
 .variables-table {
   table-layout: fixed;