What does this PR do?

This PR fixes a small bug in the conditional in modeling_marian.py. In issue #39542, the issue raiser noticed that both input_ids and input_embeds were none, but that got filtered into the conditional check for both being not None.

Related to but does not fix #39542

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Ran pytest tests/models/marian/test_modeling_marian.py to check for regressions.

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

@ArthurZucker @Rocketknight1