fixed SDXL text encoder training bug #5016 (#5078)

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

examples/dreambooth/train_dreambooth_lora_sdxl.py

@@ -1070,6 +1070,11 @@ def main(args):
         if args.train_text_encoder:
             text_encoder_one.train()
             text_encoder_two.train()
+            
+            # set top parameter requires_grad = True for gradient checkpointing works
+            text_encoder_one.text_model.embeddings.requires_grad_(True)
+            text_encoder_two.text_model.embeddings.requires_grad_(True)
+            
         for step, batch in enumerate(train_dataloader):
             with accelerator.accumulate(unet):
                 pixel_values = batch["pixel_values"].to(dtype=vae.dtype)