Fix broken CI due to missing conversion files

[ydshieh]

What does this PR do?

Fix #36267.

Marian have a few tests regarding its conversion file, but in the release branch, we remove those files and tests are failing.
I don't have clear context if we should keep these (3) tests, and marian seems to be the only model where have tests involving conversion files.

In order to be run CI with v4.49-release, we will need a patch however.

cc @Rocketknight1 for visibility.

[HuggingFaceDocBuilderDev]

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[dvrogozh]

I guess alternate solution is to separate this test out to dedicated test file and prune it along with conversion scripts on the release commit. However, I am not aware of the plans around conversion scripts in general, so I just note a possibility. Are they being deprecated and will be pruned going forward? Regardless, this change works for me in the sense that on future Transformers releases we will be able to run tests w/o explicitly ignoring some of them.

[ydshieh]

We are removing conversion scripts in the release as those cause some security reports and prevent users from enterprises from using transformers. Let's see what the other maintainers say 🤗

[Rocketknight1]

I think we can just remove the tests for conversion files entirely!

[ydshieh]

Merge it. It's only about conversion files and marian is the only model that has such tests.