fix: sampling in flax keeps EOS
Author: borisdayma
Pull request: yes

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Fixes #28377


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Comments:
Running the same example listed in #28377, we get the correct output with EOS token present before the PAD tokens:
`["


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.
<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>"]`