Replace deprecation warning f-string with class name.

When `__repr__` is invoked in the instance serialization of
`config_dict` fails, because it contains `kwargs` of type `<class
inspect._empty>`.

Author: pcuenca

src/diffusers/pipelines/stable_diffusion/pipeline_stable_diffusion.py

@@ -60,7 +60,7 @@ def __init__(
 
         if hasattr(scheduler.config, "steps_offset") and scheduler.config.steps_offset != 1:
             warnings.warn(
-                f"The configuration file of this scheduler: {scheduler} is outdated. `steps_offset`"
+                f"The configuration file of the {scheduler.__class__.__name__} scheduler is outdated. `steps_offset`"
                 f" should be set to 1 instead of {scheduler.config.steps_offset}. Please make sure "
                 "to update the config accordingly as leaving `steps_offset` might led to incorrect results"
                 " in future versions. If you have downloaded this checkpoint from the Hugging Face Hub,"

src/diffusers/pipelines/stable_diffusion/pipeline_stable_diffusion_img2img.py

@@ -72,7 +72,7 @@ def __init__(
 
         if hasattr(scheduler.config, "steps_offset") and scheduler.config.steps_offset != 1:
             warnings.warn(
-                f"The configuration file of this scheduler: {scheduler} is outdated. `steps_offset`"
+                f"The configuration file of the {scheduler.__class__.__name__} scheduler is outdated. `steps_offset`"
                 f" should be set to 1 instead of {scheduler.config.steps_offset}. Please make sure "
                 "to update the config accordingly as leaving `steps_offset` might led to incorrect results"
                 " in future versions. If you have downloaded this checkpoint from the Hugging Face Hub,"

src/diffusers/pipelines/stable_diffusion/pipeline_stable_diffusion_inpaint.py

@@ -87,7 +87,7 @@ def __init__(
 
         if hasattr(scheduler.config, "steps_offset") and scheduler.config.steps_offset != 1:
             warnings.warn(
-                f"The configuration file of this scheduler: {scheduler} is outdated. `steps_offset`"
+                f"The configuration file of the {scheduler.__class__.__name__} scheduler is outdated. `steps_offset`"
                 f" should be set to 1 instead of {scheduler.config.steps_offset}. Please make sure "
                 "to update the config accordingly as leaving `steps_offset` might led to incorrect results"
                 " in future versions. If you have downloaded this checkpoint from the Hugging Face Hub,"