No need List<Customer> in HttpEntity

[Sharofiddin]

https://github.com/rieckpil/testing-spring-boot-applications-primer/blame/214683e3bcd91e00d3125c38c59f5688bcea73a3/src/test/java/de/rieckpil/blog/exercise11/BasicIT.java#L33

Since, GET request has no body in this example, List<Customer> in HttpEntity<List<Customer>> is redundant instead Void can be used.