build(docs-infra): ensure the correct files are in the i18n example (#37947)

The Stackblitz and zip-file include `doc-files` unnecssarily and are missing
the locale files. This commit updates the `stackblitz.json` to fix this.

PR Close #37947

aio/content/examples/i18n/stackblitz.json

@@ -3,7 +3,9 @@
     "files":[
       "!**/*.d.ts",
       "!**/*.js",
-      "!**/*.[0-9].*"
+      "!**/*.[0-9].*",
+      "!doc-files/**/*",	
+      "**/*.xlf"
     ],
     "file": "src/app/app.component.ts", 
     "tags": ["Angular", "i18n", "internationalization"]