Fix optional value macro unit test

Author: andrewheard

FirebaseAI/Tests/TestApp/Packages/FirebaseAILogicExtended/Tests/FirebaseGenerableMacroTests/FirebaseGenerableTests.swift

@@ -85,11 +85,13 @@ final class FirebaseAILogicMacrosTests: XCTestCase {
             nonisolated struct Partial: Identifiable, FirebaseAILogic.ConvertibleFromModelOutput {
               var id: FirebaseAILogic.ResponseID
               var firstName: String.Partial?
+              var middleName: String?.Partial?
               var lastName: String.Partial?
               var age: Int.Partial?
               nonisolated init(_ content: FirebaseAILogic.ModelOutput) throws {
                 self.id = content.id ?? FirebaseAILogic.ResponseID()
                 self.firstName = try content.value(forProperty: "firstName")
+                self.middleName = try content.value(forProperty: "middleName")
                 self.lastName = try content.value(forProperty: "lastName")
                 self.age = try content.value(forProperty: "age")
               }