[Python] Failing test with pandas master for extension type conversion

_______________ test_conversion_extensiontype_to_extensionarray ________________

monkeypatch = <_pytest.monkeypatch.MonkeyPatch object at 0x7fcd6c580bd0>

    def test_conversion_extensiontype_to_extensionarray(monkeypatch):
        # converting extension type to linked pandas ExtensionDtype/Array
        import pandas.core.internals as _int
    
        storage = pa.array([1, 2, 3, 4], pa.int64())
        arr = pa.ExtensionArray.from_storage(MyCustomIntegerType(), storage)
        table = pa.table({'a': arr})
    
        if LooseVersion(pd.__version__) < "0.26.0.dev":
            # ensure pandas Int64Dtype has the protocol method (for older pandas)
            monkeypatch.setattr(
                pd.Int64Dtype, '__from_arrow__', _Int64Dtype__from_arrow__,
                raising=False)
    
        # extension type points to Int64Dtype, which knows how to create a
        # pandas ExtensionArray
>       result = table.to_pandas()

opt/conda/envs/arrow/lib/python3.7/site-packages/pyarrow/tests/test_pandas.py:3560: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
pyarrow/ipc.pxi:559: in pyarrow.lib.read_message
    ???
pyarrow/table.pxi:1369: in pyarrow.lib.Table._to_pandas
    ???
opt/conda/envs/arrow/lib/python3.7/site-packages/pyarrow/pandas_compat.py:764: in table_to_blockmanager
    blocks = _table_to_blocks(options, table, categories, ext_columns_dtypes)
opt/conda/envs/arrow/lib/python3.7/site-packages/pyarrow/pandas_compat.py:1102: in _table_to_blocks
    for item in result]
opt/conda/envs/arrow/lib/python3.7/site-packages/pyarrow/pandas_compat.py:1102: in <listcomp>
    for item in result]
opt/conda/envs/arrow/lib/python3.7/site-packages/pyarrow/pandas_compat.py:723: in _reconstruct_block
    pd_ext_arr = pandas_dtype.__from_arrow__(arr)
opt/conda/envs/arrow/lib/python3.7/site-packages/pandas/core/arrays/integer.py:108: in __from_arrow__
    array = array.cast(pyarrow_type)
pyarrow/table.pxi:240: in pyarrow.lib.ChunkedArray.cast
    ???
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

>   ???
E   pyarrow.lib.ArrowNotImplementedError: No cast implemented from extension<arrow.py_extension_type> to int64