Get msgpack inside Pyodide virtual environment

Author: agriyakhetarpal

.github/workflows/emscripten.yml

@@ -66,7 +66,7 @@ jobs:
           pyodide venv .venv-pyodide
           source .venv-pyodide/bin/activate
           python -m pip install dist/*.whl
-          python -m pip install pytest pytest-cov
+          python -m pip install pytest pytest-cov msgpack
           python -m pytest -v --cov=zarr --cov-config=pyproject.toml zarr
 
       - name: Upload Pyodide wheel artifact for debugging