Make contents of boost confirmation dialog scroll (#1710)

This is necessary for boosting long posts on small screens - see this post for video: https://slime.global/@masklayer/102308

app/assets/stylesheets/components.scss

@@ -2281,6 +2281,7 @@ button.icon-button.active i.fa-retweet {
 }
 
 .boost-modal__container {
+  overflow-x: scroll;
   padding: 10px;
 
   .status {