Docs: Add missing @since tags for some REST API methods added in 5.8.

Follow-up to [50995], [51021].

See #52628, #53461.

git-svn-id: https://develop.svn.wordpress.org/trunk@51280 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/rest-api/endpoints/class-wp-rest-sidebars-controller.php

@@ -365,6 +365,8 @@ class WP_REST_Sidebars_Controller extends WP_REST_Controller {
 	/**
 	 * Retrieves the block type' schema, conforming to JSON Schema.
 	 *
+	 * @since 5.8.0
+	 *
 	 * @return array Item schema data.
 	 */
 	public function get_item_schema() {