Add "Show caddy modules" in GH WF

Author: git001

.github/workflows/go.yml

@@ -27,3 +27,5 @@ jobs:
     - name: Build
       run: ./xcaddy build --with github.com/kirsch33/realip --with github.com/caddyserver/jsonc-adapter --with github.com/git001/caddyv2-upload
 
+    - name: Show caddy modules
+      run: ./caddy list-modules