Fix a missing @requires_zarr in tests (#5936)

When zarr is not available, this test fails with `NameError: name 'zarr' is not defined`.

Author: ArchangeGabriel

xarray/tests/test_backends.py

@@ -2398,6 +2398,7 @@ def create_zarr_target(self):
             yield tmp
 
 
+@requires_zarr
 @requires_fsspec
 def test_zarr_storage_options():
     pytest.importorskip("aiobotocore")