Add DateTime to typing for diff()

[cp2boston]

• [ x] I have searched the issues of this repo and believe that this is not a duplicate.
• [ x] I have searched the documentation and believe that my question is not covered.

Feature Request

This doesn't affect operations, but it does cause my linter to flag. The diff method:
`
def diff( # type: ignore[override]
self, dt: datetime.datetime | None = None, abs: bool = True
) -> Interval:
"""
Returns the difference between two DateTime objects represented as an Interval.
"""
if dt is None:
dt = self.now(self.tz)

    return Interval(self, dt, absolute=abs)

`
will complain if the dt type is a Pendulum DateTime object.