Some aggregate operations using the array API fail

What happened?

Here are some tests demonstrating the problem https://github.com/pydata/xarray/commit/9d6269de9fec4c66aeade2fdf9829c6e066a6eac:

FAILED xarray/tests/test_array_api.py::test_aggregation[max] - assert False
FAILED xarray/tests/test_array_api.py::test_aggregation[min] - assert False
FAILED xarray/tests/test_array_api.py::test_aggregation[mean] - assert False
FAILED xarray/tests/test_array_api.py::test_aggregation[prod] - assert False
FAILED xarray/tests/test_array_api.py::test_aggregation[std] - assert False
FAILED xarray/tests/test_array_api.py::test_aggregation[var] - assert False
FAILED xarray/tests/test_array_api.py::test_aggregation_skipna[std] - TypeError: std() got an unexpected keyword argument 'ddof'
FAILED xarray/tests/test_array_api.py::test_aggregation_skipna[var] - TypeError: var() got an unexpected keyword argument 'ddof'

What did you expect to happen?

No response

Minimal Complete Verifiable Example

No response

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.

Relevant log output

No response

Anything else we need to know?

No response

Environment

Start with the failing cases in xarray/tests/test_array_api.py, especially test_aggregation and test_aggregation_skipna, and run those tests at the reported commit. Trace the array API aggregate operations and compare the failures with NumPy's aggregation behavior; done means all listed max, min, mean, prod, std, and var cases pass, including skipna handling of ddof.