[gitignore] fixtures created by unit tests
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/4031?src=pr&el=h1) Report
> Merging [#4031](https://codecov.io/gh/huggingface/transformers/pull/4031?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/4e817ff41885063e08bb3bcd63e5adfd835b9911&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/4031/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/4031?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master    #4031   +/-   ##
=======================================
  Coverage   78.44%   78.44%           
=======================================
  Files         111      111           
  Lines       18518    18518           
=======================================
  Hits        14527    14527           
  Misses       3991     3991           
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/4031?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/file\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4031/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9maWxlX3V0aWxzLnB5) | `68.49% <0.00%> (-0.37%)` | :arrow_down: |
| [src/transformers/modeling\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4031/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ191dGlscy5weQ==) | `91.06% <0.00%> (+0.12%)` | :arrow_up: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/4031?src=pr&el=footer). Last update [4e817ff...361724e](https://codecov.io/gh/huggingface/transformers/pull/4031?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>Which tests yield those fixtures? I just ran all the tests and I have none of those<|||||>It comes from adding a failing test so we don't need it. My bad.