Update modeling_seamless_m4t.py SeamlessM4TForSpeechToText needs text_decoder it should not be in _keys_to_ignore_on_load_missing.
Author: alihejazi97
Pull request: yes

SpeechToText needs text decoder but not text encoder.

# What does this PR do?

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Fixes # (issue)


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Models:

- text models: @ArthurZucker
- vision models: @amyeroberts
- speech models: @sanchit-gandhi
- graph models: @clefourrier

Library:

- flax: @sanchit-gandhi
- generate: @zucchini-nlp (visual-language models) or @gante (all others)
- pipelines: @Narsil
- tensorflow: @gante and @Rocketknight1
- tokenizers: @ArthurZucker
- trainer: @muellerzr and @SunMarc

Integrations:

- deepspeed: HF Trainer/Accelerate: @muellerzr
- ray/raytune: @richardliaw, @amogkam
- Big Model Inference: @SunMarc
- quantization (bitsandbytes, autogpt): @SunMarc

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- accelerate: [different repo](https://github.com/huggingface/accelerate)
- datasets: [different repo](https://github.com/huggingface/datasets)
- diffusers: [different repo](https://github.com/huggingface/diffusers)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

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Comments:
Hi @alihejazi97, thanks for opening a PR! 

Could you provide some more context - describing the issue and linking to a related issue or sharing a code snippet which reproduces the error?

cc @ylacombe