Upgrade to Spring Kafka 2.2.8

Closes gh-17645

Author: snicoll

spring-boot-project/spring-boot-dependencies/pom.xml

@@ -170,7 +170,7 @@
 		<spring-framework.version>${spring.version}</spring-framework.version>
 		<spring-hateoas.version>0.25.2.RELEASE</spring-hateoas.version>
 		<spring-integration.version>5.1.7.RELEASE</spring-integration.version>
-		<spring-kafka.version>2.2.8.BUILD-SNAPSHOT</spring-kafka.version>
+		<spring-kafka.version>2.2.8.RELEASE</spring-kafka.version>
 		<spring-ldap.version>2.3.2.RELEASE</spring-ldap.version>
 		<spring-plugin.version>1.2.0.RELEASE</spring-plugin.version>
 		<spring-restdocs.version>2.0.3.RELEASE</spring-restdocs.version>