Migrate to JUnit 5

spring-cloud-function-context

spring-cloud-function-context: fix

spring-cloud-function-web

spring-cloud-function-adapters

spring-cloud-function-samples

spring-cloud-function-deployer; spring-cloud-function-kotlin

Resolves #535

spring-cloud-function-samples/function-sample-gcp-http/src/test/java/com/example/FunctionSampleGcpIntegrationTest.java

@@ -18,7 +18,7 @@ package com.example;
 
 import java.io.IOException;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.test.web.client.TestRestTemplate;