test: update write_empty test for zarr 3.1.2 (#10665)

Author: ianhi

xarray/tests/test_backends.py

@@ -4301,9 +4301,10 @@ def assert_expected_files(expected: list[str], store: str) -> None:
                 # that was performed by the roundtrip_dir
                 if (write_empty is False) or (write_empty is None and has_zarr_v3):
                     expected.append("1.1.0")
-                elif not has_zarr_v3:
-                    # TODO: remove zarr3 if once zarr issue is fixed
-                    # https://github.com/zarr-developers/zarr-python/issues/2931
+                elif not has_zarr_v3 or has_zarr_v3_async_oindex:
+                    # this was broken from zarr 3.0.0 until 3.1.2
+                    # async oindex released in 3.1.2 along with a fix
+                    # for write_empty_chunks in append
                     expected.extend(
                         [
                             "1.1.0",