Fix fastcgi cache caching redirect responses (#1641)

Scope fastcgi_cache_valid to 200 responses only, preventing nginx from
caching 301/302 redirects which can cause redirect loops when cached
redirect target points back through WordPress/canonical redirects.

Also add $upstream_http_location to fastcgi_no_cache as an additional
guard against caching any response with a Location header.

Closes #1594

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: retlehs

roles/wordpress-setup/templates/wordpress-site.conf.j2

@@ -252,9 +252,9 @@ server {
     {% if fastcgi_cache_enabled -%}
     # Fastcgi cache settings
     fastcgi_cache wordpress;
-    fastcgi_cache_valid {{ item.value.cache.duration | default(nginx_cache_duration) }};
+    fastcgi_cache_valid 200 {{ item.value.cache.duration | default(nginx_cache_duration) }};
     fastcgi_cache_bypass $skip_cache;
-    fastcgi_no_cache $skip_cache;
+    fastcgi_no_cache $skip_cache $upstream_http_location;
     fastcgi_cache_background_update {{ item.value.cache.background_update | default(nginx_cache_background_update) }};
 
     {% endif -%}