Fix the tests for Electra
Add the tests for `TFElectraForSequenceClassification` and `TFElectraForMultipleChoice` and fix them.
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/6284?src=pr&el=h1) Report
> Merging [#6284](https://codecov.io/gh/huggingface/transformers/pull/6284?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/c67d1a0259cbb3aef31952b4f37d4fee0e36f134&el=desc) will **decrease** coverage by `0.00%`.
> The diff coverage is `100.00%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/6284/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/6284?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #6284      +/-   ##
==========================================
- Coverage   79.19%   79.18%   -0.01%     
==========================================
  Files         147      147              
  Lines       27120    27120              
==========================================
- Hits        21478    21476       -2     
- Misses       5642     5644       +2     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/6284?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/modeling\_electra.py](https://codecov.io/gh/huggingface/transformers/pull/6284/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19lbGVjdHJhLnB5) | `81.55% <100.00%> (ø)` | |
| [src/transformers/generation\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/6284/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9nZW5lcmF0aW9uX3RmX3V0aWxzLnB5) | `81.70% <0.00%> (-5.02%)` | :arrow_down: |
| [src/transformers/modeling\_tf\_electra.py](https://codecov.io/gh/huggingface/transformers/pull/6284/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl9lbGVjdHJhLnB5) | `94.24% <0.00%> (+4.71%)` | :arrow_up: |

------

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> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/6284?src=pr&el=footer). Last update [c67d1a0...1c5c550](https://codecov.io/gh/huggingface/transformers/pull/6284?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>I would like to use `TFElectraForSequenceClassification`

I assume I would need to install from source.
Any info on when the next release to pypi will be ? 

Thanks!<|||||>@nemani It will be available in the next few days 