fix: base64 decoding in attach decorator

aries_cloudagent/messaging/decorators/attach_decorator.py

@@ -288,7 +288,7 @@ class AttachDecoratorData(BaseModel):
         """Accessor for signed content (payload), None for unsigned."""
 
         return (
-            b64_to_bytes(unpad(set_urlsafe_b64(self.base64, urlsafe=True)))
+            b64_to_bytes(unpad(set_urlsafe_b64(self.base64, urlsafe=True)), True)
             if self.signatures
             else None
         )