Install xarray in documentation builds

Author: WardBrian

.github/workflows/release.yml

@@ -32,7 +32,7 @@ jobs:
 
       - name: Install dependencies (python)
         run: |
-          python -m pip install --upgrade pip wheel twine codecov "sphinx>4,<5" nbsphinx ipython ipykernel "pydata-sphinx-theme<0.9" requests sphinx-copybutton matplotlib
+          python -m pip install --upgrade pip wheel twine codecov "sphinx>4,<5" nbsphinx ipython ipykernel "pydata-sphinx-theme<0.9" requests sphinx-copybutton xarray matplotlib
           pip install -r requirements.txt
           pip install -e .