has_attentions - consistent test skipping logic and tf tests
# What does this PR do?

Two linked changes regarding the control of tests being run: 

**PyTorch and TF consistency**: `has_attentions` flag is used in `test_modeling_common.py` to control some of the logic in tests that are run, only applying them if the model has attention(s). This PR adds equivalent logic to tests in `test_modeling_tf_common.py`

**Skipping tests consistency**: `unittest.skip` is used to skip entire tests if they cannot/do not apply to that model e.g. for [input embedding test in ConvNext](https://github.com/huggingface/transformers/blob/f394a2a50d8729cd1ca9b368e330ec50664c3292/tests/models/convnext/test_modeling_convnext.py#L161). For `test_attention_outputs` this was controlled with an if-else statement. This was changed to be controlled with `unittest.skip` instead for two reasons: 1) consistency with the rest of the code base 2) prevent confusing pytest outputs i.e. models without attention are shown to skip `test_attention_outputs` instead of passing it. 

## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [ ] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [x] Did you write any new necessary tests?

_The documentation is not available anymore as the PR was closed or merged._<|||||>@NielsRogge, @ydshieh, @patrickvonplaten adding you to cover: git blame ownership, test ownership, some git blame and general transformers ownership. I hope that's OK. Feel free to remove yourselves and/or add others you think are more suitable.  <|||||>Thanks a lot for cleaning this up @amyeroberts ! <|||||>@NielsRogge  I decide not to remove `has_attentions` in this PR, and would like to focus on making the PT/TF test consistency. If that's OK with you, I'll go ahead and merge. 