Allow getting-started to scroll on short screens (#10075)

At 480px height, there is not enough space to fully display the footer.

app/javascript/styles/mastodon/components.scss

@@ -2336,6 +2336,7 @@ a.account__display-name {
 
 .getting-started {
   color: $dark-text-color;
+  overflow: auto;
 
   &__footer {
     flex: 0 0 auto;