refactor: remove dead zarr<3 (has_zarr_v3) guards in tests (#11376)

* refactor: remove dead zarr<3 (has_zarr_v3) guards in tests

* fix: keep has_zarr short-circuit in zarr-format helpers for zarr-less envs

---------

Co-authored-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>

Author: mvanhorn

xarray/tests/__init__.py

@@ -131,10 +131,10 @@ def _importorskip(
 has_bottleneck, requires_bottleneck = _importorskip("bottleneck")
 has_rasterio, requires_rasterio = _importorskip("rasterio")
 has_zarr, requires_zarr = _importorskip("zarr")
-has_zarr_v3, requires_zarr_v3 = _importorskip("zarr", "3.0.0")
+requires_zarr_v3 = requires_zarr
 has_zarr_v3_dtypes, requires_zarr_v3_dtypes = _importorskip("zarr", "3.1.0")
 has_zarr_v3_async_oindex, requires_zarr_v3_async_oindex = _importorskip("zarr", "3.1.2")
-if has_zarr_v3:
+if has_zarr:
     import zarr
 
     # manual update by checking attrs for now
@@ -197,14 +197,7 @@ def _importorskip(
     "zarr_format",
     [
         pytest.param(2, id="zarr_format=2"),
-        pytest.param(
-            3,
-            marks=pytest.mark.skipif(
-                not has_zarr_v3,
-                reason="zarr-python v2 cannot understand the zarr v3 format",
-            ),
-            id="zarr_format=3",
-        ),
+        pytest.param(3, id="zarr_format=3"),
     ],
 )