Fix recurring mock data

Reusing the faker instance like I used to seems to (suddenly?!)
result in the same data, which newly results in a conflict response

tests/Vegasco.Server.Api.Tests.Integration/CarFaker.cs

@@ -5,15 +5,15 @@ namespace Vegasco.Server.Api.Tests.Integration;
 
 internal class CarFaker
 {
-	private readonly Faker _faker = new();
-
 	internal CreateCar.Request CreateCarRequest()
 	{
-		return new CreateCar.Request(_faker.Person.FirstName);
+		Faker faker = new();
+		return new CreateCar.Request(faker.Person.FirstName);
 	}
 
 	internal UpdateCar.Request UpdateCarRequest()
 	{
-		return new UpdateCar.Request(_faker.Person.FirstName);
+		Faker faker = new();
+		return new UpdateCar.Request(faker.Person.FirstName);
 	}
 }