fixing NettyRoutingFilterIntegrationTests

[rjuare8]

Fix NettyRoutingFilter tests by migrating error message config to Spring Boot 4 key

While running the Spring Cloud Gateway server WebFlux tests on the current
Spring Boot 4 / Spring Cloud 2025 snapshot, I hit failures in
NettyRoutingFilterIntegrationTests.shouldApplyGlobalResponseTimeoutForInvalidRouteTimeoutValue().

This test asserts that the error response body contains a top-level
message field with the timeout text:

.expectBody()
    .jsonPath("$.status")
    .isEqualTo(String.valueOf(HttpStatus.GATEWAY_TIMEOUT.value()))
    .jsonPath("$.message")
    .isEqualTo("Response took longer than timeout: PT3S");

However, after the upgrade, the legacy configuration key:

server:
  error:
    include-message: always

is no longer supported. Spring Boot now expects the new
spring.web.error.include-message property and ignores the old key,
emitting a migration warning. As a result, the default behavior is to
omit the message attribute from the error JSON, causing the JsonPath
assertion on $.message to fail even though the gateway behavior is
otherwise correct.

This PR updates the test configuration to use the new property so that
the error message field is once again included in the response body
and the tests can validate the timeout message as intended.

Summary of changes

spring-cloud-gateway-server-webflux/src/test/resources/application-netty-routing-filter.yml
spring-cloud-gateway-server-webflux/src/test/resources/application.yml:

- server:
-   error:
-     include-message: always
+ spring:
+   web:
+     error:
+       include-message: always

Motivation

After the Spring Boot / Spring Cloud upgrade, the deprecated
server.error.include-message key is no longer honored and triggers a
migration warning. This silently changes the shape of the error JSON by
removing the message field, breaking tests that assert on that field.

Migrating the configuration to spring.web.error.include-message
restores the previous behavior (making the error message available to
clients and tests), keeps the tests stable across environments, and
removes the “configuration keys that are no longer supported” warnings
from the test logs.