Add missing close quotation mark

Author: andrewheard

FirebaseVertexAI/Sources/GenerativeAIService.swift

@@ -213,7 +213,7 @@ struct GenerativeAIService {
   private func httpResponse(urlResponse: URLResponse) throws -> HTTPURLResponse {
     // The following condition should always be true: "Whenever you make HTTP URL load requests, any
     // response objects you get back from the URLSession, NSURLConnection, or NSURLDownload class
-    // are instances of the HTTPURLResponse class.
+    // are instances of the HTTPURLResponse class."
     guard let response = urlResponse as? HTTPURLResponse else {
       VertexLog.error(
         code: .generativeAIServiceNonHTTPResponse,