Fix: Prevent double title issue in SEO metadata by updating seo.html (#4959)

Author: alouiadel

_includes/seo.html

@@ -2,7 +2,11 @@
 {%- assign title_separator = site.title_separator | default: '-' -%}
 
 {%- assign page_title = page.title | default: site.title | replace: '|', '|' -%}
-{%- assign seo_title = page_title | append: " " | append: title_separator | append: " " | append: site.title | replace: '|', '|' -%}
+{%- if page_title contains site.title -%}
+  {%- assign seo_title = page_title | replace: '|', '|' -%}
+{%- else -%}
+  {%- assign seo_title = page_title | append: " " | append: title_separator | append: " " | append: site.title | replace: '|', '|' -%}
+{%- endif -%}
 
 {%- assign page_title = page_title | markdownify | strip_html | strip_newlines | escape_once -%}
 {%- assign seo_title  = seo_title  | markdownify | strip_html | strip_newlines | escape_once -%}