Test: Consider testing GCSFS

[ianhi]

Currently it seems that zarr with a gcsfs backend is not tested. See

zarr-python/tests/test_store/test_fsspec.py

Lines 23 to 28 in 5968fc7

	fsspec = pytest.importorskip("fsspec")
	s3fs = pytest.importorskip("s3fs")
	requests = pytest.importorskip("requests")
	moto_server = pytest.importorskip("moto.moto_server.threaded_moto_server")
	moto = pytest.importorskip("moto")
	botocore = pytest.importorskip("botocore")

If it's easy to generalize the test class it would be nice to also test GCSFS