Update Font Awesome to v6.5.1 and replace Twitter icon with X icon

Co-authored-by: ckenst <6896787+ckenst@users.noreply.github.com>

Author: Copilot

_includes/head.html

@@ -8,7 +8,8 @@
     content="{% if page.excerpt %}{{ page.excerpt | strip_html | strip_newlines | truncate: 160 }}{% else %}{{ site.description }}{% endif %}">
 
   <link rel="stylesheet" href="{{ "/css/main.css" | prepend: site.baseurl }}">
-  <link rel="stylesheet" href="/css/font-awesome/css/font-awesome.min.css">
+  <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.1/css/all.min.css" crossorigin="anonymous" referrerpolicy="no-referrer">
+  <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.1/css/v4-shims.min.css" crossorigin="anonymous" referrerpolicy="no-referrer">
   <link rel="canonical" href="{{ page.url | replace:'index.html','' | prepend: site.baseurl | prepend: site.url }}">
   <link rel="alternate" type="application/rss+xml" title="{{ site.title }}" href="{{ "/feed.xml" | prepend:
     site.baseurl | prepend: site.url }}" />