fix doc building error.

Author: sayakpaul

src/diffusers/pipelines/sana/__init__.py

@@ -38,6 +38,7 @@
         from .pipeline_sana import SanaPipeline
         from .pipeline_sana_controlnet import SanaControlNetPipeline
         from .pipeline_sana_sprint import SanaSprintPipeline
+        from .pipeline_sana_sprint_img2img import SanaSprintImg2ImgPipeline
 else:
     import sys