add back set_attention_backend

src/diffusers/models/attention.py

@@ -160,6 +160,16 @@ class AttentionModuleMixin:
         """
         if not return_deprecated_lora:
             return self.processor
+    
+    def set_attention_backend(self, backend: str):
+        from .attention_dispatch import AttentionBackendName
+
+        available_backends = {x.value for x in AttentionBackendName.__members__.values()}
+        if backend not in available_backends:
+            raise ValueError(f"`{backend=}` must be one of the following: " + ", ".join(available_backends))
+
+        backend = AttentionBackendName(backend.lower())
+        self.processor._attention_backend = backend
 
     def set_use_npu_flash_attention(self, use_npu_flash_attention: bool) -> None:
         """