Upgrade to Kafka 2.8.0

As part of the upgrade, a switch to Spring Kafka 2.8.0-SNAPSHOT is
required, see gh-27177

Closes gh-27247

spring-boot-project/spring-boot-dependencies/build.gradle

@@ -993,7 +993,7 @@ bom {
 			]
 		}
 	}
-	library("Kafka", "2.7.1") {
+	library("Kafka", "2.8.0") {
 		group("org.apache.kafka") {
 			modules = [
 				"connect-api",
@@ -1677,7 +1677,7 @@ bom {
 			]
 		}
 	}
-	library("Spring Kafka", "2.7.2") {
+	library("Spring Kafka", "2.8.0-SNAPSHOT") {
 		group("org.springframework.kafka") {
 			modules = [
 				"spring-kafka",