Start building against Spring Session Bean snapshots

See gh-14333

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

@@ -171,7 +171,7 @@
 		<spring-restdocs.version>2.0.2.RELEASE</spring-restdocs.version>
 		<spring-retry.version>1.2.2.RELEASE</spring-retry.version>
 		<spring-security.version>5.1.0.BUILD-SNAPSHOT</spring-security.version>
-		<spring-session-bom.version>Bean-M2</spring-session-bom.version>
+		<spring-session-bom.version>Bean-BUILD-SNAPSHOT</spring-session-bom.version>
 		<spring-ws.version>3.0.3.RELEASE</spring-ws.version>
 		<sqlite-jdbc.version>3.23.1</sqlite-jdbc.version>
 		<statsd-client.version>3.1.0</statsd-client.version>