Make interpolate_2d handle datetime64 correctly
Broken off from #27626 because I decided that is poorly scoped.
Test added, unnecessary piece removed.  No release note needed since no user-facing changes. > datetime64[ns]-dtype. datetime with TZ seems fine
> DataFrame.interpolate. Series[datetime64[ns]].interpolate seems fine

I'm not sure I understand your example.  Is it relevant that you passed tz to date_range?  You subsequently astype-d it away.

Best guess: DatetimeTZBlock.fillna dispatches to DatetimeArray.fillna, so doesn't go directly through here. @jreback gentle ping.  Between this and the quantile PR, we're about to be about to be able to rip out a bunch of _try_coerce_result code thanks