bundles/nginx: only add well-known alias for vhosts which use letsencrypt

bundles/nginx/files/site_template

@@ -74,9 +74,11 @@ server {
 % endif
     add_header Permissions-Policy interest-cohort=();
 
+%   if ssl == 'letsencrypt':
     location /.well-known/acme-challenge/ {
         alias /var/lib/dehydrated/acme-challenges/;
     }
+%   endif
 
 % if security_txt:
     location = /.well-known/security.txt {