[CI] Address Hugo deprecation warning: use hugo.IsMultilingual (#4962)

Author: chalin

layouts/partials/i18n/fallback-page.html

@@ -1,15 +1,14 @@
 {{/*
 
-  Returns the fallback page of this page, if it has one.
-  A fallback page, is a page in the default site language
-  that has been mounted under this locale as a fallback
-  when this locale is missing a translation.
+  Returns the fallback page of this page, if it has one. A fallback page is a
+  page in the default site language that has been mounted under this locale as a
+  fallback when this locale is missing a translation.
 
 */ -}}
 
 {{ $result := false -}}
 
-{{ if and .Site.IsMultiLingual .File -}}
+{{ if and hugo.IsMultilingual .File -}}
   {{ $defaultLang := .Site.Sites.Default.Language.Lang -}}
 
   {{ $resultsArray := where .Translations "Lang" $defaultLang -}}