Fix doctests

Author: dstansby

docs/usage_zarr_v2.md

@@ -331,7 +331,7 @@ try:
 except ValidationError as exc:
     print(exc)
     """
-    1 validation error for GroupSpec[GroupAttrs, TypeVar]
+    1 validation error for GroupSpec[GroupAttrs, ~TItem]
     attributes.b
       Input should be a valid integer, unable to parse string as an integer [type=int_parsing, input_value='foo', input_type=str]
         For further information visit https://errors.pydantic.dev/2.6/v/int_parsing
@@ -350,7 +350,7 @@ try:
 except ValidationError as exc:
     print(exc)
     """
-    1 validation error for GroupSpec[TypeVar, ArraySpec]
+    1 validation error for GroupSpec[~TAttr, ArraySpec]
     members.foo
       Input should be a valid dictionary or instance of ArraySpec [type=model_type, input_value=GroupSpec(zarr_version=2,...tributes={}, members={}), input_type=GroupSpec]
         For further information visit https://errors.pydantic.dev/2.6/v/model_type