Move __basePath script to _header.html where template context exists

_head.html is included without context (no dot), so {{.Site.BaseURL}}
rendered as empty string. _header.html gets the full context.

Author: jonathanpopham

templates/_head.html

@@ -6,4 +6,3 @@
 <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=Public+Sans:wght@200;300;400;500;600;700&family=Martian+Mono:wght@300;400;500&family=Lexend+Peta:wght@400&display=swap" rel="stylesheet">
-<script>var __basePath = (function() { try { return new URL("{{.Site.BaseURL}}").pathname.replace(/\/$/, ""); } catch(e) { return ""; } })();</script>

templates/_header.html

@@ -1,3 +1,4 @@
+<script>var __basePath = (function() { try { return new URL("{{.Site.BaseURL}}").pathname.replace(/\/$/, ""); } catch(e) { return ""; } })();</script>
 <a href="#main-content" class="skip-link">Skip to content</a>
 <header class="site-header">
   <div class="container">