Test type promotion in elementwise/operator tests

[honno]

@asmeurer has already said to me that he found the granular type promotion tests useful when developing numpy.array_api, but I think it'd be nice if the primary tests also did this anyway.

• An implementer might rely on the primary test when developing an elwise/op function, so end up missing the type promotion errors.
• xfailing test_type_promotion.py tests is annoying by way of how it parametrizes (e.g. I'm finding this for Clear up CI #49), so it'd be nice if we could have a CI job that only runs the primary tests (as they should implicitly cover the type promotion and signature tests).