Source

File: wp-includes/rest-api/endpoints/class-wp-rest-revisions-controller.php

public function get_items_permissions_check( $request ) {
		$parent = $this->get_parent( $request['parent'] );
		if ( is_wp_error( $parent ) ) {
			return $parent;
		}

		if ( ! current_user_can( 'edit_post', $parent->ID ) ) {
			return new WP_Error(
				'rest_cannot_read',
				__( 'Sorry, you are not allowed to view revisions of this post.' ),
				array( 'status' => rest_authorization_required_code() )
			);
		}

		return true;
	}