Potential fix for code scanning alert no. 24: Incomplete string escaping or encoding (#1661)

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

Author: kueken

sourcefiles/modern/plugins/jquery/jquery-ui-1.12.1.js

@@ -1561,7 +1561,7 @@ var keycode = $.ui.keyCode = {
 
 // Internal use only
 var escapeSelector = $.ui.escapeSelector = ( function() {
-	var selectorEscape = /([!"#$%&'()*+,./:;<=>?@[\]^`{|}~])/g;
+	var selectorEscape = /([!"#$%&'()*+,./:;<=>?@[\\\]^`{|}~])/g;
 	return function( selector ) {
 		return selector.replace( selectorEscape, "\\$1" );
 	};