ci: fix failing healthcheck after keycloak update

The latest keycloak version exposes health and metrics on the management
interface listening on 9090 by default.

Also get rid of the warning: URL(string) deprecated in java.

docker-compose.yml

@@ -11,7 +11,7 @@ services:
     volumes:
       - ./tests/realms:/opt/keycloak/data/import
     healthcheck:
-      test: ['CMD-SHELL', '[ -f /tmp/HealthCheck.java ] || echo "public class HealthCheck { public static void main(String[] args) throws java.lang.Throwable { System.exit(java.net.HttpURLConnection.HTTP_OK == ((java.net.HttpURLConnection)new java.net.URL(args[0]).openConnection()).getResponseCode() ? 0 : 1); } }" > /tmp/HealthCheck.java && java /tmp/HealthCheck.java http://localhost:8080/health/live']
+      test: ['CMD-SHELL', '[ -f /tmp/HealthCheck.java ] || echo "public class HealthCheck { public static void main(String[] args) throws java.lang.Throwable { System.exit(java.net.HttpURLConnection.HTTP_OK == ((java.net.HttpURLConnection)new java.net.URI(args[0]).toURL().openConnection()).getResponseCode() ? 0 : 1); } }" > /tmp/HealthCheck.java && java /tmp/HealthCheck.java http://localhost:9000/health/live']
       interval: 10s
       timeout: 5s
       retries: 3