HOTFIX: drop vietnamese translation

Author: burtenshaw

.github/workflows/build_documentation.yml

@@ -14,6 +14,6 @@ jobs:
       package_name: mcp-course
       path_to_docs: mcp-course/units/
       additional_args: --not_python_module
-      languages: en vi
+      languages: en
     secrets:
-      hf_token: ${{ secrets.HF_DOC_BUILD_PUSH }}
+      hf_token: ${{ secrets.HF_DOC_BUILD_PUSH }}