Run array API tests on Zarr 2 (#730)

Author: tomwhite

.github/workflows/array-api-tests.yml

@@ -44,6 +44,7 @@ jobs:
         run: |
           pushd array-api-tests
           pip install -e '../cubed[test]'
+          pip install -U 'zarr<3'
           pip install -r requirements.txt  # from Array API tests repo
       - name: Run Array API tests
         env: