Fix gRpc test

Signed-off-by: Oleg Zhurakousky <oleg.zhurakousky@broadcom.com>

Author: olegz

spring-cloud-gateway-integration-tests/grpc/src/test/java/org/springframework/cloud/gateway/tests/grpc/JsonToGrpcApplicationTests.java

@@ -40,6 +40,9 @@
 
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.boot.test.web.server.LocalServerPort;
+import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.MediaType;
 import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
 import org.springframework.web.client.RestTemplate;
 
@@ -72,9 +75,11 @@ public void shouldConvertFromJSONToGRPC() {
 		configurer.addRoute(grpcServerPort, "/json/hello",
 				"JsonToGrpc=file:src/main/proto/hello.pb,file:src/main/proto/hello.proto,HelloService,hello");
 
+		HttpHeaders headers = new HttpHeaders();
+		headers.setContentType(MediaType.APPLICATION_JSON);
+		HttpEntity<String> request = new HttpEntity<>("{\"firstName\":\"Duff\", \"lastName\":\"McKagan\"}", headers);
 		String response = restTemplate
-			.postForEntity("https://localhost:" + this.gatewayPort + "/json/hello",
-					"{\"firstName\":\"Duff\", \"lastName\":\"McKagan\"}", String.class)
+			.postForEntity("https://localhost:" + this.gatewayPort + "/json/hello", request, String.class)
 			.getBody();
 
 		Assertions.assertThat(response).isNotNull();