[LED Test] fix common inputs pt for flaky pt-tf led test

[patrickvonplaten]

What does this PR do?

Fixes flaky led test: tests/test_modeling_tf_led.py::TFLEDModelTest::test_pt_tf_model_equivalence. 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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[patrickvonplaten]

@LysandreJik @sgugger - should fix flaky TFLED test.

[sgugger]

Thanks!