Possible redundant assertion in test_validate

Hi,

There appear to be a duplicate assertion in [test_validate](https://github.com/marshmallow-code/marshmallow-oneofschema/blob/main/tests/test_one_of_schema.py#L278), which I'm not sure is intentional?

Open tests/test_one_of_schema.py at test_validate around line 278 and compare the nearby assertions to determine whether one is duplicated. Check the surrounding test intent before deciding whether the redundant assertion should be removed, then run the relevant test file to confirm the test suite still passes.

Written by the indexing model from the issue text.