Add AttentionMixin to WanVACETransformer3DModel

to enable methods like `set_attn_processor()`.

Author: J4BEZ

src/diffusers/models/transformers/transformer_wan_vace.py

@@ -134,7 +134,9 @@ def forward(
         return conditioning_states, control_hidden_states
 
 
-class WanVACETransformer3DModel(ModelMixin, ConfigMixin, PeftAdapterMixin, FromOriginalModelMixin, CacheMixin):
+class WanVACETransformer3DModel(
+    ModelMixin, ConfigMixin, PeftAdapterMixin, FromOriginalModelMixin, CacheMixin, AttentionMixin
+):
     r"""
     A Transformer model for video-like data used in the Wan model.