Fix styling issue on /about when server admin has a long username (#15357)

Co-authored-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/styles/mastodon/about.scss

@@ -732,6 +732,7 @@ $small-breakpoint: 960px;
 
       &__column {
         flex: 1 1 50%;
+        overflow-x: hidden;
       }
     }