Install docs dependencies for tests, refs #1153

.github/workflows/test.yml

@@ -29,7 +29,7 @@ jobs:
         (cd tests && gcc ext.c -fPIC -shared -o ext.so)
     - name: Install dependencies
       run: |
-        pip install -e '.[test]'
+        pip install -e '.[test,docs]'
         pip freeze
     - name: Run tests
       run: |