Fix expected value for OPT test `test_inference_no_head`
# What does this PR do?

- Update the expected value in the test `OPTModelIntegrationTests.test_inference_no_head` to have more precisions
- Lower atol to `5e-5`

On GPU VM, the test has to be run with TF32 disabled (or without TF32 support).

See: https://pytorch.org/docs/stable/notes/cuda.html
Related discussion: #16588
_The documentation is not available anymore as the PR was closed or merged._