Issue #3436514: Log warning instead of error in case of non existing media...

Issue #3436514: Log warning instead of error in case of non existing media embeds in media embed filter

Closes #3436514

core/modules/media/src/Plugin/Filter/MediaEmbed.php

@@ -298,7 +298,7 @@ public function process($text, $langcode) {
       $media = $this->entityRepository->loadEntityByUuid('media', $uuid);
       assert($media === NULL || $media instanceof MediaInterface);
       if (!$media) {
-        $this->loggerFactory->get('media')->error('During rendering of embedded media: the media item with UUID "@uuid" does not exist.', ['@uuid' => $uuid]);
+        $this->loggerFactory->get('media')->warning('During rendering of embedded media: the media item with UUID "@uuid" does not exist.', ['@uuid' => $uuid]);
       }
       else {
         $media = $this->entityRepository->getTranslationFromContext($media, $langcode);