Fix nginx /id endpoint on Fedora 43

Fedora 43's nginx.conf introduces an inline default server block on
port 80 before the conf.d include, causing our server block to lose
priority and return 404. Adding default_server to the listen directives
ensures our server handles port 80 traffic regardless of definition
order. This is harmless on Fedora 42 where no competing server exists.

Assisted-by: Claude Opus 4.6
Signed-off-by: Eduardo Olivares <eolivare@redhat.com>

Author: eduolivares

artifacts/tobiko-images/conf/nginx_id.conf

@@ -1,5 +1,5 @@
 server{
-    listen 80;
-    listen [::]:80;
+    listen 80 default_server;
+    listen [::]:80 default_server;
     location /id { add_header Content-Type text/plain; return 200 '$hostname';}
 }