Fix `test_tf_encode_plus_sent_to_model` for `LayoutLMv3`
# What does this PR do?

The recently added `TFLayoutLMv3Model` triggered the test `test_tf_encode_plus_sent_to_model`, which needs to prepare an extra argument `boxes` when calling tokenizer methods, otherwise we get an error

```bash
>               for word, box in zip(text, boxes):
E               TypeError: 'NoneType' object is not iterable
```

[Currently failed test](https://github.com/huggingface/transformers/runs/8173669915?check_suite_focus=true)
_The documentation is not available anymore as the PR was closed or merged._<|||||>A question -- PT has an equivalent tokenizer test, yet I don't see this test being overwritten in PT's `layoutlmv3`. Do you know why that happens? 🤔 <|||||>> A question -- PT has an equivalent tokenizer test, yet I don't see this test being overwritten in PT's layoutlmv3. Do you know why that happens?

Hi @gante I guess you are talking about 
https://github.com/huggingface/transformers/blob/dae0bfc525dd9867a2c9f5917cbf551fb9cc1732/tests/models/layoutlmv3/test_tokenization_layoutlmv3.py#L1154
(I didn't realized there is a PT version for this test until now)

That test method uses `boxes` (and overwrites the common one), see
https://github.com/huggingface/transformers/blob/dae0bfc525dd9867a2c9f5917cbf551fb9cc1732/tests/models/layoutlmv3/test_tokenization_layoutlmv3.py#L1185

I can change this PR to be more like that PT test.<|||||>Oh, right! I was looking for the test in the wrong file :)