TST: Fix 36 maybe_promote xfails wanting np.bytes_ instead of np.object_
@jreback less trivial than some of the others.  These changes are based on my understanding that maybe_promote should _never_ be returning np.bytes_ dtype; those cases all become np.object_.  That is what maybe_promote currently does, and this updates the tests to expect that behavior.
we should never have bytes as these are not a pandas supported dtype; anything that is not a standard (str, int, float, m8, M8 etc, or EA dtype) would just promote to object 

bytes are not special in that regard > we should never have bytes as these are not a pandas supported dtype

agreed, that matches what this PR does.  The xfailed tests that this fixes do _not_ match what you said thanks