Fix flakey test

[MAILPOET-2890]

lib/Cron/Workers/KeyCheck/SendingServiceKeyCheck.php

@@ -27,6 +27,9 @@ class SendingServiceKeyCheck extends KeyCheckWorker {
     return Bridge::isMPSendingServiceEnabled();
   }
 
+  /**
+   * @return \DateTimeInterface|Carbon
+   */
   public function getNextRunDate() {
     // when key pending approval, check key sate every hour
     if ($this->servicesChecker->isMailPoetAPIKeyPendingApproval()) {

tests/integration/Cron/Workers/KeyCheck/SendingServiceKeyCheckTest.php

@@ -34,7 +34,8 @@ class SendingServiceKeyCheckTest extends \MailPoetTest {
 
   public function testItRunsEveryHourWhenKeyPendingApproval() {
     // normally next run is scheduled at a start of next day
-    expect($this->worker->getNextRunDate())->equals(Carbon::now()->startOfDay()->addDay());
+    expect($this->worker->getNextRunDate()->format('Y-m-d H:i:s'))
+      ->equals(Carbon::now()->startOfDay()->addDay()->format('Y-m-d H:i:s'));
 
     // when pending key approval, next run is scheduled in an hour
     $settings = $this->diContainer->get(SettingsController::class);