test fix loading spinner problem

https://github.com/storybookjs/storybook/issues/17838

alfa-client/libs/design-system/nginx.conf

@@ -32,7 +32,7 @@ http {
        
 
         location / {
-            root   /usr/share/nginx/html/design-system;
+            root   /usr/share/nginx/html/design-system/;
             index  index.html index.htm;
 
             add_header Cache-Control "no-store, no-cache, must-revalidate, proxy-revalidate, max-age=0";