Editor: Fix undefined variable following [54805].

Props mamaduka, costdev, mukesh27.
See #56974, #57067.


git-svn-id: https://develop.svn.wordpress.org/trunk@55142 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-theme-json.php

@@ -2111,7 +2111,7 @@ public function get_styles_for_block( $block_metadata ) {
 					// support features use the same custom selector.
 					if ( isset( $feature_declarations[ $feature_selector ] ) ) {
 						foreach ( $new_feature_declarations as $new_feature_declaration ) {
-							$feature_declarations[ $feature_selector ][] = $feature_declaration;
+							$feature_declarations[ $feature_selector ][] = $new_feature_declaration;
 						}
 					} else {
 						$feature_declarations[ $feature_selector ] = $new_feature_declarations;