Fix WebFluxDslTests for SF changes

Author: artembilan

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)
-				.body("{\"name\": \"\"}")
+				.bodyValue("{\"name\": \"\"}")
 				.exchange()
 				.expectStatus().isBadRequest();