implementing tflxmertmodel integration test
What does this PR do?
this PR implement an integration test for TFLxmertmodel as requested in [#9954](https://github.com/huggingface/transformers/issues/9954)

@LysandreJik
I believe your version of the code quality tools isn't up to date - can you try running the following at the root of your clone: `pip install -e .[quality] -U` to update your tools?<|||||>Hi @LysandreJik  Yep It was my black version