Fix JavaScript console error on Getting Started column (#19891)

* Fix JavaScript console error on Getting Started column

* Update app/javascript/mastodon/components/column_header.js

Co-authored-by: Ilias Tsangaris <iliastsangaris@gmail.com>

Co-authored-by: Ilias Tsangaris <iliastsangaris@gmail.com>

app/javascript/mastodon/components/column_header.js

@@ -57,7 +57,7 @@ class ColumnHeader extends React.PureComponent {
   }
 
   handleTitleClick = () => {
-    this.props.onClick();
+    this.props.onClick?.();
   }
 
   handleMoveLeft = () => {