gateway 进行Dubbo 调用，设置了Route 降级，降级后返回httpstatus 为 200 ，内容为空，而不是设置的返回状态，调整多个设置都无用

## Issue Description
通过 Route ID 设置了 降级后，在gatewayFilter 通过dubbo调用 鉴权服务，鉴权服务返回错误后，首次通过接口调用返回状态 500 是正常，但降级后，**返回状态是 200 ，字符为空**，
- filter 设置了 Mono 返回 也无效
- 在 ErrorWebExceptionHandler 获取到了 ParamFlowException ，按照 [这篇文章的](https://github.com/alibaba/Sentinel/issues/2049)，设置了自定义返回 Mono 也无效，依然改变了我设置的返回状态和内容
- 未进入 BlockRequestHandler

错误信息，但拦截错误，设置了返回状态也无用：
com.alibaba.csp.sentinel.slots.block.flow.param.ParamFlowException: $D
Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException:
Error has been observed at the following site(s):
|_ checkpoint ⇢ springfox.boot.starter.autoconfigure.SwaggerUiWebFluxConfiguration$CustomWebFilter [DefaultWebFilterChain]
|_ checkpoint ⇢ org.springframework.web.cors.reactive.CorsWebFilter [DefaultWebFilterChain]
|_ checkpoint ⇢ org.springframework.cloud.gateway.filter.WeightCalculatorWebFilter [DefaultWebFilterChain]
|_ checkpoint ⇢ org.springframework.boot.actuate.metrics.web.reactive.server.MetricsWebFilter [DefaultWebFilterChain]
|_ checkpoint ⇢ HTTP GET "/demo/dubbo/echo" [ExceptionHandlingWebHandler]
Stack trace:

### Tell us your environment

org.springframework.cloud
spring-cloud-starter-gateway
2.2.3.RELEASE

com.alibaba.cloud
spring-cloud-starter-alibaba-sentinel
2.2.5.RELEASE

com.alibaba.cloud
spring-cloud-alibaba-sentinel-gateway
2.2.5.RELEASE

### Anything else we need to know?
如何设置，才能返回我设置的状态 和 内容？或者还有其他解决方案吗？

Start by reproducing the Route ID downgrade on /demo/dubbo/echo with the listed Spring Cloud Gateway and Sentinel dependencies. Inspect the gatewayFilter, ErrorWebExceptionHandler, and BlockRequestHandler behavior around ParamFlowException; done means the configured HTTP status and response content remain after downgrade.

Written by the indexing model from the issue text.