[DreamBooth] Set train mode for text encoder (huggingface#1012)

Set train mode for text encoder

Author: duongna21

examples/dreambooth/train_dreambooth.py

@@ -574,6 +574,8 @@ def collate_fn(examples):
 
     for epoch in range(args.num_train_epochs):
         unet.train()
+        if args.train_text_encoder:
+            text_encoder.train()
         for step, batch in enumerate(train_dataloader):
             with accelerator.accumulate(unet):
                 # Convert images to latent space