Start building against Spring Kafka 4.0.0 snapshots

See gh-47829

platform/spring-boot-dependencies/build.gradle

@@ -2477,7 +2477,7 @@ bom {
 			releaseNotes("https://github.com/spring-projects/spring-integration/releases/tag/v{version}")
 		}
 	}
-	library("Spring Kafka", "4.0.0-RC1") {
+	library("Spring Kafka", "4.0.0-SNAPSHOT") {
 		considerSnapshots()
 		group("org.springframework.kafka") {
 			modules = [

starter/spring-boot-starter-kafka-test/build.gradle

@@ -23,9 +23,7 @@ description = "Starter for testing Apache Kafka"
 dependencies {
 	api(project(":starter:spring-boot-starter-kafka"))
 	api(project(":starter:spring-boot-starter-test"))
-	api("org.springframework.kafka:spring-kafka-test") {
-		exclude group: "org.apache.logging.log4j", module: "log4j-slf4j-impl"
-	}
+	api("org.springframework.kafka:spring-kafka-test")
 }
 
 checkRuntimeClasspathForConflicts {