test_resize_tokens_embeddings does not inspect `get_output_embeddings`
Here is the existing logic: copied below for convenience
https://github.com/huggingface/transformers/blob/bbf26c4e619cf42106163e1e2cd5ff98b936ff93/tests/test_modeling_common.py#L489)

```python
model_embed = model.resize_token_embeddings(config.vocab_size)
cloned_embeddings = model_embed.weight.clone()
# Check that resizing the token embeddings with a larger vocab size increases the model's vocab size
model_embed = model.resize_token_embeddings(model_vocab_size + 10)
self.assertEqual(model.config.vocab_size, model_vocab_size + 10)
self.assertEqual(model_embed.weight.shape[0], cloned_embeddings.shape[0] + 10)
```

Since we never test the return value of `get_output_embeddings` after resizing, the model can avoid setting it to the new vocab size. 
BART did this by overwriting `tie_weights` to do nothing (fix proposed in https://github.com/huggingface/transformers/pull/3323)



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