Fix concurrent modification exception with dispatcher caching

keycloak-1  | 2024-06-21 08:32:21,335 ERROR [org.keycloak.services.error.KeycloakErrorHandler] (executor-thread-9) Uncaught server error: java.util.ConcurrentModificationException
keycloak-1  | 	at java.base/java.util.HashMap.computeIfAbsent(HashMap.java:1221)
keycloak-1  | 	at sh.libre.scim.core.ScimDispatcher.createForSession(ScimDispatcher.java:31)
keycloak-1  | 	at sh.libre.scim.event.ScimEventListenerProvider.<init>(ScimEventListenerProvider.java:49)
keycloak-1  | 	at sh.libre.scim.event.ScimEventListenerProviderFactory.create(ScimEventListenerProviderFactory.java:13)
keycloak-1  | 	at sh.libre.scim.event.ScimEventListenerProviderFactory.create(ScimEventListenerProviderFactory.java:9)
keycloak-1  | 	at org.keycloak.services.DefaultKeycloakSession.getProvider(DefaultKeycloakSession.java:195)