dont mutate metadata/tags (#19742)

libs/core/langchain_core/prompts/base.py

@@ -112,9 +112,9 @@ class BasePromptTemplate(
     ) -> PromptValue:
         config = ensure_config(config)
         if self.metadata:
-            config["metadata"].update(self.metadata)
+            config["metadata"] = {**config["metadata"], **self.metadata}
         if self.tags:
-            config["tags"].extend(self.tags)
+            config["tags"] = config["tags"] + self.tags
         return self._call_with_config(
             self._format_prompt_with_error_handling,
             input,