fix(deps): update spring core to v6

Author: renovate[bot]

gradle.properties

@@ -2,7 +2,7 @@ group=org.jasig.portlet.notification
 version=4.8.1-SNAPSHOT
 
 # Matches (apparently) Spring Boot 1.5.10.RELEASE
-springVersion=4.3.30.RELEASE
+springVersion=6.2.6
 springSecurityVersion=4.2.9.RELEASE
 springSecurityOAuth2Version=2.5.2.RELEASE