Update custom.html to add fetch priority for font

This PR increases the fetch priority for the google font so that it loads faster. This increases lighthouse performance.

_includes/head/custom.html

@@ -2,7 +2,7 @@
 <link rel="icon" href="/images/favicon.ico" type="image/x-icon">
 <link rel="preconnect" href="https://fonts.googleapis.com">
 <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
-<link href="https://fonts.googleapis.com/css2?family=Itim&family=Poppins:wght@100;200;300;400;500;600;700;800;900&display=swap" rel="stylesheet" async>
+<link href="https://fonts.googleapis.com/css2?family=Itim&family=Poppins:wght@100;200;300;400;500;600;700;800;900&display=swap" rel="stylesheet" async fetchpriority="high">
 
 <!-- Matomo -->
 <script type="text/javascript">