langchain[patch]: update llm_router.py (#18865)

Issue : _call method of LLMRouterChain uses predict_and_parse, which is
slated for deprecation.

Description : Instead of using predict_and_parse, this replaces it with
individual predict and parse functions.

libs/langchain/langchain/chains/router/llm_router.py

@@ -56,9 +56,11 @@ def _call(
     ) -> Dict[str, Any]:
         _run_manager = run_manager or CallbackManagerForChainRun.get_noop_manager()
         callbacks = _run_manager.get_child()
+
+        prediction = self.llm_chain.predict(callbacks=callbacks, **inputs)
         output = cast(
             Dict[str, Any],
-            self.llm_chain.predict_and_parse(callbacks=callbacks, **inputs),
+            self.llm_chain.prompt.output_parser.parse(prediction),
         )
         return output