[ci] install fairscale on self-runner CIs
The tests for the new sharded ddp fairscale integration are in place, https://github.com/huggingface/transformers/pull/9177
but CIs don't have `fairscale` installed so they won't run on CI. 

This is an issue to track this need so we will eventually run these tests.

Blocking event: needing a more reliable/quick way of installing fairscale - need to track the following issue for when this happens:
https://github.com/facebookresearch/fairscale/issues/264

Then we can add `pip install fairscale` to the self-runner CIs with multigpus.
Probably should change CI to do:
```
pip install fairscale --no-build-isolation
```
which is much faster then the new pip system, as it doesn't need to fetch dependent packages
<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.