Add a warning when using xarray_beam.ChunksToZarr with no template

If this works well at some point in the future (e.g., using zarr v3), we can always remove the warning. But for now, this is better than letting users run directly into the race condition in #85

I've also removed all suggestions from the docs of omitting a `template`.

PiperOrigin-RevId: 721163016

Author: shoyer

.github/workflows/ci-build.yml

@@ -23,21 +23,23 @@ jobs:
       with:
         access_token: ${{ github.token }}
       if: ${{github.ref != 'refs/head/main'}}
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v5
       with:
         python-version: ${{ matrix.python-version }}
     - name: Get pip cache dir
       id: pip-cache
       run: |
         python -m pip install --upgrade pip wheel
-        echo "dir=$(pip cache dir)" >> "$GITHUB_OUTPUT"
+        echo "::set-output name=dir::$(pip cache dir)"
     - name: pip cache
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: ${{ steps.pip-cache.outputs.dir }}
         key: ${{ runner.os }}-pip-${{ hashFiles('**/setup.py') }}
+        restore-keys: |
+          ${{ runner.os }}-pip-
     - name: Install Xarray-Beam
       run: |
         pip install -e .[tests]