Clear ProducesRequestCondition cache attribute

As of spring-projects/spring-framework#22644, Spring Framework caches
the "produces" condition when matching for endpoints in the
`HandlerMapping` infrastructure. This has been improved in
spring-projects/spring-framework#23091 to prevent side-effects in other
implementations.

Prior to this commit, the Spring Boot actuator infrastructure for
`EndpointHandlerMapping` would not clear the cached attribute,
presenting the same issue as Spring Framework's infrastructure. This
means that a custom arrangement with custom `HandlerMapping` or
`ContentTypeResolver` would not work properly and reuse the cached
produced conditions for other, unintented, parts of the handler mapping
process.

This commit clears the cached data and ensures that other handler
mapping implementations are free of that side-effect.

Fixes gh-20150

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/reactive/AbstractWebFluxEndpointHandlerMapping.java

@@ -198,6 +198,12 @@ protected CorsConfiguration initCorsConfiguration(Object handler, Method method,
 		return this.corsConfiguration;
 	}
 
+	@Override
+	public Mono<HandlerMethod> getHandlerInternal(ServerWebExchange exchange) {
+		return super.getHandlerInternal(exchange)
+				.doOnTerminate(() -> ProducesRequestCondition.clearMediaTypesAttribute(exchange));
+	}
+
 	@Override
 	protected boolean isHandler(Class<?> beanType) {
 		return false;

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/servlet/AbstractWebMvcEndpointHandlerMapping.java

@@ -231,6 +231,16 @@ protected CorsConfiguration initCorsConfiguration(Object handler, Method method,
 		return this.corsConfiguration;
 	}
 
+	@Override
+	protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
+		try {
+			return super.getHandlerInternal(request);
+		}
+		finally {
+			ProducesRequestCondition.clearMediaTypesAttribute(request);
+		}
+	}
+
 	@Override
 	protected boolean isHandler(Class<?> beanType) {
 		return false;