Update combined.py (#7541)

from my understanding, the `check_repeated_memory_variable` validator
will raise an error if any of the variables in the `memories` list are
repeated. However, the `load_memory_variables` method does not check for
repeated variables. This means that it is possible for the
`CombinedMemory` instance to return a dictionary of memory variables
that contains duplicate values. This code will check for repeated
variables in the `data` dictionary returned by the
`load_memory_variables` method of each sub-memory. If a repeated
variable is found, an error will be raised.

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---------

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

libs/langchain/langchain/memory/combined.py

@@ -61,10 +61,12 @@ def load_memory_variables(self, inputs: Dict[str, Any]) -> Dict[str, str]:
         # Collect vars from all sub-memories
         for memory in self.memories:
             data = memory.load_memory_variables(inputs)
-            memory_data = {
-                **memory_data,
-                **data,
-            }
+            for key, value in data.items():
+                if key in memory_data:
+                    raise ValueError(
+                        f"The variable {key} is repeated in the CombinedMemory."
+                    )
+                memory_data[key] = value
 
         return memory_data