BUG: groupby.resample index is 32-bit on 64-bit Windows when grouping by Python ints

[rhshadrach]

In the code below, the first level of the index of result comes out as a 32-bit integer on 64-bit Windows. On 64-bit Linux, it is 64-bit as expected.

df = DataFrame(
    index=Index(
        pd.to_datetime(
            ["2018-01-01 00:00:00", "2018-01-01 12:00:00", "2018-01-02 00:00:00"]
        ),
        name="date",
    )
)
result = df.groupby([0, 0, 1]).resample(rule=pd.to_timedelta("06:00:00")).mean()