MINOR: [Python] Mention interval in the is_temporal docstring

[Nishuuzz]

pyarrow.types.is_temporal() returns True for interval types, but its docstring doesn't say so:

>>> import pyarrow as pa, pyarrow.types as t
>>> t.is_temporal(pa.month_day_nano_interval())
True
>>> t.is_temporal.__doc__.strip().splitlines()[0]
'Return True if value is an instance of type: date, time, timestamp or duration.'

That's the documented contract being narrower than the behaviour, and since these docstrings are generated from the @doc(is_null, datatype=...) decorator they're what ends up on the API docs page.

Including interval is deliberate rather than accidental — _TEMPORAL_TYPES is built as

_TEMPORAL_TYPES = ({lib.Type_TIMESTAMP,
                    lib.Type_DURATION} | _TIME_TYPES | _DATE_TYPES |
                   _INTERVAL_TYPES)

and test_is_temporal_date_time_timestamp already asserts types.is_temporal(pa.month_day_nano_interval()). So this is a docs fix, not a behaviour question; I've only changed the datatype string.

After the change the rendered line is

Return True if value is an instance of type: date, time, timestamp, duration or interval.

which is exactly the set that returns True — I checked each one (date32, time32, timestamp, duration, interval all True; int32 False) by applying the same edit to an installed pyarrow and reading the generated docstring back.

I found this while comparing every predicate set in types.py against the corresponding arrow::is_*() in cpp/src/arrow/type_traits.h, the same way GH-50847 turned up. Worth noting the two is_temporal definitions genuinely differ — the C++ one covers only date/time/timestamp, while Python also counts duration and interval — but that's a semantic question rather than something to change quietly in a MINOR PR, so I've left it alone and only made the Python docstring match the Python behaviour.