Report cron error message where possible

Author: fredden

app/code/Magento/Cron/Observer/ProcessCronQueueObserver.php

@@ -366,7 +366,7 @@ function () use ($schedule) {
             );
             if (!$e instanceof \Exception) {
                 $e = new \RuntimeException(
-                    'Error when running a cron job',
+                    'Error when running a cron job: ' . $e->getMessage(),
                     0,
                     $e
                 );

app/code/Magento/Cron/Test/Unit/Observer/ProcessCronQueueObserverTest.php

@@ -617,7 +617,7 @@ function ($callback) {
      */
     public function dispatchExceptionInCallbackDataProvider(): array
     {
-        $throwable = new TypeError();
+        $throwable = new TypeError('Description of TypeError');
         return [
             'non-callable callback' => [
                 'Not_Existed_Class',
@@ -640,11 +640,11 @@ public function dispatchExceptionInCallbackDataProvider(): array
                 new CronJobException(
                     $throwable
                 ),
-                'Error when running a cron job',
+                'Error when running a cron job: Description of TypeError',
                 2,
                 1,
                 new \RuntimeException(
-                    'Error when running a cron job',
+                    'Error when running a cron job: Description of TypeError',
                     0,
                     $throwable
                 )