fix(core): fix strict schema generation for functions with optional args

libs/core/langchain_core/utils/function_calling.py

@@ -460,6 +460,8 @@ def convert_to_openai_function(
                     parameters = dict(parameters)
                     parameters["required"] = list(fields.keys())
                     oai_function["parameters"] = parameters
+            oai_function["parameters"]["additionalProperties"] = False
+
     return oai_function