Update train_controlnet_flux.py,Fix size mismatch issue in validation (#9679)

Update train_controlnet_flux.py

Fix the problem of inconsistency between size of image and size of validation_image which causes np.stack to report error.
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>

examples/controlnet/train_controlnet_flux.py

@@ -152,6 +152,7 @@ def log_validation(
                     guidance_scale=3.5,
                     generator=generator,
                 ).images[0]
+            image = image.resize((args.resolution, args.resolution))
             images.append(image)
         image_logs.append(
             {"validation_image": validation_image, "images": images, "validation_prompt": validation_prompt}