Move fonts to the header.php

`@import` is discouraged because it's blocking.

Signed-off-by: XhmikosR <xhmikosr@gmail.com>

scripts/pi-hole/php/header.php

@@ -200,6 +200,7 @@
     <meta name="msapplication-TileImage" content="img/logo.svg">
     <meta name="apple-mobile-web-app-capable" content="yes">
 
+    <link rel="stylesheet" href="style/vendor/SourceSansPro/SourceSansPro.css">
     <link rel="stylesheet" href="style/vendor/bootstrap/css/bootstrap.min.css">
 
     <link rel="stylesheet" href="style/vendor/font-awesome-5.11.2/css/all.min.css">

style/vendor/AdminLTE.min.css

@@ -1,4 +1,4 @@
-@import url(SourceSansPro/SourceSansPro.css);/*!
+/*!
  *   AdminLTE v2.1.2
  *   Author: Almsaeed Studio
  *	 Website: Almsaeed Studio <http://almsaeedstudio.com>