Fix phpstan error courtesy of the laravel 11 upgrade (changed signatures and return types)

app/Services/FireflyIIIOrg/Update/UpdateRequest.php

@@ -117,7 +117,7 @@ class UpdateRequest implements UpdateRequestInterface
         // parse response a bit. No message yet.
         $response          = $json['firefly_iii'][$channel];
         $date              = Carbon::createFromFormat('Y-m-d', $response['date']);
-        if (false === $date) {
+        if (null === $date) {
             $date = today(config('app.timezone'));
         }
         $return['version'] = $response['version'];