Fix error responses handling in WebClient

This commit fixes a typo in the `DefaultWebClient` implementation.
Instead of forwarding resolved `WebClientException` instances as error
signals, the `bodyToMono(ParameterizedTypeReference)` variant would just
forward those exceptions as `onNext` signals.

Issue: SPR-15946

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/DefaultWebClient.java

@@ -422,7 +422,7 @@ class DefaultWebClient implements WebClient {
 		public <T> Mono<T> bodyToMono(ParameterizedTypeReference<T> typeReference) {
 			return this.responseMono.flatMap(
 					response -> bodyToMono(response, BodyExtractors.toMono(typeReference),
-							mono -> (Mono<T>)mono));
+							this::monoThrowableToMono));
 		}
 
 		private <T> Mono<T> monoThrowableToMono(Mono<? extends Throwable> mono) {