fix nightly ci (#2801)

packages/typespec-test/test/openai_modular/spec/models/completions/chat_messages.tsp

@@ -111,6 +111,7 @@ model ChatRequestUserMessage extends ChatRequestMessage {
   role: ChatRole.user;
 
   @doc("The contents of the user message, with available input types varying by selected model.")
+  @added(ServiceApiVersions.v2024_02_15_Preview)
   content: ChatMessageContent;
 
   @doc("An optional name for the participant.")