Fixed Typo in modeling_bart.py
# What does this PR do?

Fixes #11895 
Fixed Typo `(seq_len, batch, embed_dim)` to `(batch, seq_len, embed_dim)`  in line 
[373](https://github.com/huggingface/transformers/blob/996a315e76f6c972c854990e6114226a91bc0a90/src/transformers/models/bart/modeling_bart.py#L373) and [376](https://github.com/huggingface/transformers/blob/996a315e76f6c972c854990e6114226a91bc0a90/src/transformers/models/bart/modeling_bart.py#L376) as discussed [here](https://github.com/huggingface/transformers/issues/11895).

@NielsRogge 

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Models:

- albert, bert, xlm: @LysandreJik
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Thanks a lot for fixing this!

Could you run `make fix-copies` and then push again?