Return early if should not be sent to social media

Return early and don't send the post to social media if the `Post to
social media` checkbox is not checked.

References #249

web/modules/custom/blog/src/EventSubscriber/PushBlogPostToSocialMedia.php

@@ -53,6 +53,10 @@ final class PushBlogPostToSocialMedia implements EventSubscriberInterface {
       return;
     }
 
+    if (!$entity->shouldSendToSocialMedia()) {
+      return;
+    }
+
     // If this post has already been sent to social media, do not send it again.
     if ($entity->hasBeenSentToSocialMedia()) {
       return;