[Core] Public page missing title fix (#7121)

Fix public pages with missing an HTML title because the template is using the incorrect variable name.

smarty/templates/public_layout.tpl

@@ -8,7 +8,7 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
   <meta http-equiv="X-UA-Compatible" content="ie=edge">
-  <title>{$page_title}</title>
+  <title>{$study_title}</title>
   <link rel="stylesheet" href="{$baseurl}/bootstrap/css/bootstrap.min.css">
   <link rel="stylesheet" href="{$baseurl}/css/public_layout.css">
   <link type="image/x-icon" rel="icon" href="{$baseurl}/images/favicon.ico">