Fix “Back” button sometimes redirecting out of Mastodon (#25281)

app/javascript/mastodon/components/column_back_button.jsx

@@ -23,9 +23,7 @@ export default class ColumnBackButton extends PureComponent {
 
     if (onClick) {
       onClick();
-    // Check if there is a previous page in the app to go back to per https://stackoverflow.com/a/70532858/9703201
-    // When upgrading to V6, check `location.key !== 'default'` instead per https://github.com/remix-run/history/blob/main/docs/api-reference.md#location
-    } else if (router.route.location.key) {
+    } else if (router.history.location?.state?.fromMastodon) {
       router.history.goBack();
     } else {
       router.history.push('/');