add `sentencepiece` to requirements.txt for SD3 dreambooth (#8538)

* add `sentencepiece` requirement for SD3

add `sentencepiece` requirement

* Empty-Commit

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Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>

examples/dreambooth/requirements_sd3.txt

@@ -5,3 +5,4 @@ ftfy
 tensorboard
 Jinja2
 peft==0.11.1
+sentencepiece
\ No newline at end of file