failing type checking CI

[keewis]

Due to the update of pytest, mypy reports errors:

xarray/tests/test_cftimeindex_resample.py:57: error: List or tuple expected as variable arguments
xarray/tests/test_dataset.py:2407: error: No overload variant of "__call__" of "_XfailMarkDecorator" matches argument type "Type[AssertionError]"
xarray/tests/test_dataset.py:2407: note: Possible overload variant:
xarray/tests/test_dataset.py:2407: note:     def __call__(self, condition: Union[str, bool] = ..., *conditions: Union[str, bool], reason: str = ..., run: bool = ..., raises: Union[BaseException, Tuple[BaseException, ...]] = ..., strict: bool = ...) -> MarkDecorator
xarray/tests/test_dataset.py:2407: note:     <1 more non-matching overload not shown>
xarray/tests/test_dask.py:767: error: No overload variant of "__call__" of "_XfailMarkDecorator" matches argument type "Type[NotImplementedError]"
xarray/tests/test_dask.py:767: note: Possible overload variant:
xarray/tests/test_dask.py:767: note:     def __call__(self, condition: Union[str, bool] = ..., *conditions: Union[str, bool], reason: str = ..., run: bool = ..., raises: Union[BaseException, Tuple[BaseException, ...]] = ..., strict: bool = ...) -> MarkDecorator
xarray/tests/test_dask.py:767: note:     <1 more non-matching overload not shown>
xarray/tests/test_dataarray.py:3953: error: No overload variant of "__call__" of "_XfailMarkDecorator" matches argument type "Type[AssertionError]"
xarray/tests/test_dataarray.py:3953: note: Possible overload variant:
xarray/tests/test_dataarray.py:3953: note:     def __call__(self, condition: Union[str, bool] = ..., *conditions: Union[str, bool], reason: str = ..., run: bool = ..., raises: Union[BaseException, Tuple[BaseException, ...]] = ..., strict: bool = ...) -> MarkDecorator
xarray/tests/test_dataarray.py:3953: note:     <1 more non-matching overload not shown>
Found 4 errors in 4 files (checked 124 source files)

since that particular pytest version is a release candidate, should we pin pytest for now?

[keewis]

both types of errors are fixed on pytest master so it should be possible to pin pytest and remove the pin once 6.0.0 was released.

[keewis]

this seems to have been a mistake in the conda feedstock