[LED Test] fix common inputs pt for flaky pt-tf led test
Author: patrickvonplaten
Pull request: yes

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Fixes flaky led test: [tests/test_modeling_tf_led.py::TFLEDModelTest::test_pt_tf_model_equivalence](https://app.circleci.com/pipelines/github/huggingface/transformers/18159/workflows/e39565cd-188f-406a-bc8c-3db64a5829c5/jobs/146772/steps). It's the classic bug for Longformer, I forgot to set the global attention mask correctly for the common inputs for PT


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Comments:
@LysandreJik @sgugger - should fix flaky TFLED test.

Thanks!