Fix test fetching for examples
# What does this PR do?

When re-working the circleCI config to execute test fetching first, I didn't do anything special for the examples, which means that if only an example file is modified, no tests are run (by default only tests found in the tests subfolder are kept, for the examples we need to add `--filters tests examples`.

You can check on [this report](https://github.com/huggingface/transformers/runs/8604472112) that when only example files are modifier, the tests for all examples are still run (next step would be to properly filter between TF/Flax and PyTorch but this is going to take slightly longer).
_The documentation is not available anymore as the PR was closed or merged._