train flux_controlnet code need to update

This code is just for instantx controlnet, not suitable xlabs

https://github.com/huggingface/diffusers/blob/aa14f090f86c9641abf2da761f39a88133b49f09/examples/controlnet/train_controlnet_flux.py#L1258-L1266

reference FluxControlNetPipeline code:
https://github.com/huggingface/diffusers/blob/aa14f090f86c9641abf2da761f39a88133b49f09/src/diffusers/pipelines/flux/pipeline_flux_controlnet.py#L907-L922

Start with examples/controlnet/train_controlnet_flux.py around lines 1258-1266 and compare it with src/diffusers/pipelines/flux/pipeline_flux_controlnet.py around lines 907-922. Determine what differs between the InstantX and XLabs ControlNet paths, then update the training code so XLabs training follows the referenced pipeline behavior.

Scritto dal modello di indicizzazione a partire dal testo della issue.