Fix dropdown arrow position (#8637)

app/javascript/styles/mastodon/components.scss

@@ -1666,14 +1666,14 @@ a.account__display-name {
 
   &.top {
     bottom: -5px;
-    margin-left: -13px;
+    margin-left: -7px;
     border-width: 5px 7px 0;
     border-top-color: $ui-secondary-color;
   }
 
   &.bottom {
     top: -5px;
-    margin-left: -13px;
+    margin-left: -7px;
     border-width: 0 7px 5px;
     border-bottom-color: $ui-secondary-color;
   }