Fix parameter bug of handler inside the filterFunction DSL

Co-authored-by: hojongs <hojong.jjh@gmail.com>
Co-authored-by: bjh970913 <bjh970913@gmail.com>

Closes gh-26838

spring-webflux/src/test/kotlin/org/springframework/web/reactive/function/server/CoRouterFunctionDslTests.kt

@@ -152,6 +152,16 @@ class CoRouterFunctionDslTests {
 		}
 	}
 
+	@Test
+	fun filtering() {
+		val mockRequest = get("https://example.com/filter").build()
+		val request = DefaultServerRequest(MockServerWebExchange.from(mockRequest), emptyList())
+		StepVerifier.create(sampleRouter().route(request).flatMap { it.handle(request) })
+			.expectNextMatches { response ->
+				response.headers().getFirst("foo") == "bar"
+			}
+			.verifyComplete()
+	}
 
 	private fun sampleRouter() = coRouter {
 		(GET("/foo/") or GET("/foos/")) { req -> handle(req) }
@@ -186,6 +196,18 @@ class CoRouterFunctionDslTests {
 		path("/baz", ::handle)
 		GET("/rendering") { RenderingResponse.create("index").buildAndAwait() }
 		add(otherRouter)
+		add(filterRouter)
+	}
+
+	private val filterRouter = coRouter {
+		"/filter" { request ->
+			ok().header("foo", request.headers().firstHeader("foo")).buildAndAwait()
+		}
+
+		filter { request, next ->
+			val newRequest = ServerRequest.from(request).apply { header("foo", "bar") }.build()
+			next(newRequest)
+		}
 	}
 
 	private val otherRouter = router {