Resolve deprecations in WebFlux module

Author: artembilan

spring-integration-webflux/src/main/java/org/springframework/integration/webflux/outbound/WebFluxRequestExecutingMessageHandler.java

@@ -340,7 +340,7 @@ else if (publisherElementType instanceof ParameterizedTypeReference<?>) {
 
 	@Nullable
 	@SuppressWarnings("unchecked")
-	private BodyInserters.FormInserter<?> buildBodyInserterForMultiValueMap(
+	private static BodyInserters.FormInserter<?> buildBodyInserterForMultiValueMap(
 			MultiValueMap<?, ?> requestBody, MediaType contentType) {
 
 		if (MediaType.APPLICATION_FORM_URLENCODED.equals(contentType)) {

spring-integration-webflux/src/test/java/org/springframework/integration/webflux/dsl/WebFluxDslTests.java

@@ -313,7 +313,7 @@ public void testValidation() {
 		this.webTestClient.post().uri("/validation")
 				.headers(headers -> headers.setBasicAuth("guest", "guest"))
 				.contentType(MediaType.APPLICATION_JSON)
-				.syncBody("{\"name\": \"\"}")
+				.body("{\"name\": \"\"}")
 				.exchange()
 				.expectStatus().isBadRequest();