Change onboarding flow in web UI (#32998)

app/javascript/mastodon/components/column_back_button.tsx

@@ -24,7 +24,7 @@ function useHandleClick(onClick?: OnClickCallback) {
   }, [history, onClick]);
 }
 
-export const ColumnBackButton: React.FC<{ onClick: OnClickCallback }> = ({
+export const ColumnBackButton: React.FC<{ onClick?: OnClickCallback }> = ({
   onClick,
 }) => {
   const handleClick = useHandleClick(onClick);