Fix timeline banners sizing (#34171)

app/javascript/styles/mastodon/components.scss

@@ -9288,6 +9288,7 @@ noscript {
   border: 1px solid $highlight-text-color;
   background: rgba($highlight-text-color, 0.15);
   overflow: hidden;
+  flex-shrink: 0;
 
   &__background-image {
     width: 125%;