Real-time collaboration: fix comment syncing in site editor.

Developed in WordPress#10981.
See also WordPress/gutenberg#75746.

Props alecgeatches, czarate.
See #64622.

git-svn-id: https://develop.svn.wordpress.org/trunk@61704 602fd350-edb4-49c9-b593-d223f7449a82

Author: ellatrix

src/wp-includes/collaboration/class-wp-http-polling-sync-server.php

@@ -278,6 +278,11 @@ private function can_user_sync_entity_type( string $entity_kind, string $entity_
 			return isset( $taxonomy->cap->assign_terms ) && current_user_can( $taxonomy->cap->assign_terms );
 		}
 
+		// Handle single comment entities with a defined object ID.
+		if ( 'root' === $entity_kind && 'comment' === $entity_name && is_numeric( $object_id ) ) {
+			return current_user_can( 'edit_comment', (int) $object_id );
+		}
+
 		// All the remaining checks are for collections. If an object ID is provided,
 		// reject the request.
 		if ( null !== $object_id ) {