fix: sampling in flax keeps EOS

[borisdayma]

What does this PR do?

Fixes #28377

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[borisdayma]

Running the same example listed in #28377, we get the correct output with EOS token present before the PAD tokens:
["</s><s><s>My friends are cool but they eat too many carbs. I love carbs. The carb-averse among us have a love for dessert on this one. I've got some amazing desserts. I've been a junkie for 10 years. I can't go straight after dinner, I've been eating for 4. I love it. That's why I made the TV show.</s><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad><pad>"]

[gante]

LGTM, thank you for the fix!

[ArthurZucker]

Thanks! Not generation tests were failing? 🤗 would expect some to include testing against decoded version. Could you run for Llama for example?

[sanchit-gandhi]

Thanks for the fix @borisdayma!