[SeamlessM4Tv2] Fix links in README

[xenova]

What does this PR do?

Fixes links for SeamlessM4Tv2 model in the README.

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• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

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@sanchit-gandhi

[ArthurZucker]

Thanks, cc @ylacombe