[Glitch] Fix styling of boost button in media modal not reflecting ability to boost

Port tootsuite#16387 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/styles/components/media.scss

@@ -320,6 +320,13 @@
           background: rgba($gold-star, 0.3);
         }
       }
+
+      &.disabled {
+        color: $white;
+        background-color: transparent;
+        cursor: default;
+        opacity: 0.4;
+      }
     }
   }
 }