External Libraries: Update the Backbone.js library to version 1.6.0.

This updates the `backbone` library from version `1.5.0` to `1.6.0`. This is a minor bug fix release.

The full list of changes can be found in the Backbone.js change log: https://backbonejs.org/#changelog.

Props manooweb mardroid.
Fixes #60512.

git-svn-id: https://develop.svn.wordpress.org/trunk@58872 602fd350-edb4-49c9-b593-d223f7449a82

package.json

@@ -144,7 +144,7 @@
 		"@wordpress/warning": "3.0.1",
 		"@wordpress/widgets": "4.0.6",
 		"@wordpress/wordcount": "4.0.1",
-		"backbone": "1.5.0",
+		"backbone": "1.6.0",
 		"clipboard": "2.0.11",
 		"core-js-url-browser": "3.6.4",
 		"element-closest": "^3.0.2",

src/wp-includes/script-loader.php

@@ -1040,7 +1040,7 @@ function wp_default_scripts( $scripts ) {
 	did_action( 'init' ) && $scripts->add_data( 'json2', 'conditional', 'lt IE 8' );
 
 	$scripts->add( 'underscore', "/wp-includes/js/underscore$dev_suffix.js", array(), '1.13.4', 1 );
-	$scripts->add( 'backbone', "/wp-includes/js/backbone$dev_suffix.js", array( 'underscore', 'jquery' ), '1.5.0', 1 );
+	$scripts->add( 'backbone', "/wp-includes/js/backbone$dev_suffix.js", array( 'underscore', 'jquery' ), '1.6.0', 1 );
 
 	$scripts->add( 'wp-util', "/wp-includes/js/wp-util$suffix.js", array( 'underscore', 'jquery' ), false, 1 );
 	did_action( 'init' ) && $scripts->localize(