Change the color of the message dot on the feedback button to yellow.

This is as discussed in openwebwork#939 (post merge).

htdocs/js/Problem/problem.scss

@@ -165,7 +165,7 @@
 			left: 100%;
 			border: 1px solid black;
 			border-radius: 50%;
-			background-color: #dc3545;
+			background-color: var(--bs-warning);
 			padding: 0.25rem;
 		}
 	}