Set spring.cloud.gateway.forwarded.by.enabled=true

See gh-2658

Author: spencergibb

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/test/GatewayIntegrationTests.java

@@ -62,7 +62,7 @@
 import static org.springframework.boot.test.context.SpringBootTest.WebEnvironment.RANDOM_PORT;
 import static org.springframework.cloud.gateway.test.TestUtils.getMap;
 
-@SpringBootTest(webEnvironment = RANDOM_PORT)
+@SpringBootTest(webEnvironment = RANDOM_PORT, properties = "spring.cloud.gateway.forwarded.by.enabled=true")
 @DirtiesContext
 @SuppressWarnings("unchecked")
 @ExtendWith(OutputCaptureExtension.class)