Fix bug saving embeddings

[jeffpicard]

Hi! I have a one-liner fix suggestion.

I get the following error when running relatively straightforward scripts:

    embeddings.save_embeddings(use_state_dict=False)
  File "/code/flair/flair/embeddings/base.py", line 101, in save_embeddings
    params = self.to_params()
             ^^^^^^^^^^^^^^^^
  File "/code/flair/flair/embeddings/transformer.py", line 1359, in to_params
    del config_dict["_attn_implementation_autoset"]
        ~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
KeyError: '_attn_implementation_autoset'

Here's a minimal reproduction of the bug:

from flair.embeddings import TransformerDocumentEmbeddings
embeddings = TransformerDocumentEmbeddings(model="distilbert-base-uncased")
embeddings.save_embeddings()

This fails on master but succeeds on this branch.

I think this accidentally came in from this recent PR.

[jeffpicard]

@helpmefindaname what do you think?

[stefan-it]

I can confirm this bug when fine-tuning e.g. BERT-based models - and this PR fixes it, many thanks @jeffpicard !

[jeffpicard]

Oh great, and thank you both for fixing the CI error in #3565.

Although it looks like the download page is back up. So CI should pass on this branch if you rerun it and that PR may no longer be necessary.

[jeffpicard]

This diff was included in PR #3548 which merged, making this PR unnecessary. Closing.