[Tests] Fix opt integration test
Author: patrickvonplaten
Pull request: yes

# What does this PR do?

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Fixes failing circle ci: `tests/models/opt/test_modeling_opt.py::OPTModelIntegrationTests::test_inference_no_head`


## Before submitting
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Models:

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Comments:
_The documentation is not available anymore as the PR was closed or merged._

Let's see whether this fixes the CI