(WP 6.4-compat) Add missing type schema attribute in WP 6.4 compat'…

…s `block-hooks.php` (#55138)

* Add missing `type` attribute in WP 6.4 compat's `block-hooks.php`
* Type is required for API schemas

lib/compat/wordpress-6.4/block-hooks.php

@@ -290,6 +290,7 @@ function gutenberg_register_block_hooks_rest_field() {
 		array(
 			'schema' => array(
 				'description'       => __( 'This block is automatically inserted near any occurence of the block types used as keys of this map, into a relative position given by the corresponding value.', 'gutenberg' ),
+				'type'              => 'object',
 				'patternProperties' => array(
 					'^[a-zA-Z0-9-]+/[a-zA-Z0-9-]+$' => array(
 						'type' => 'string',