[YouTube] Extract shorts thumbnails from thumbnailViewModel

Fixes an issue, where shorts thumbnails where not extracted, as they're now
contained within a `thumbnailViewModel`, instead of a simple `thumbnail`
object.

Closes: TeamNewPipe/NewPipe#12907

Author: FineFindus

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/extractors/YoutubeShortsLockupInfoItemExtractor.java

@@ -78,7 +78,10 @@ public String getUrl() throws ParsingException {
     @Nonnull
     @Override
     public List<Image> getThumbnails() throws ParsingException {
-        return getImagesFromThumbnailsArray(shortsLockupViewModel.getObject("thumbnail")
+        return getImagesFromThumbnailsArray(shortsLockupViewModel
+                .getObject("thumbnailViewModel")
+                .getObject("thumbnailViewModel")
+                .getObject("image")
                 .getArray("sources"));
     }