Add button to dismiss desktop notifications permissions banner (#15141)

app/javascript/styles/mastodon/components.scss

@@ -7204,6 +7204,13 @@ noscript {
   flex-direction: column;
   align-items: center;
   justify-content: center;
+  position: relative;
+
+  &__close {
+    position: absolute;
+    top: 10px;
+    right: 10px;
+  }
 
   h2 {
     font-size: 16px;