Update postgres Docker tag to v13.18 (#1325)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

manifests/keycloak/values.yaml

@@ -41,7 +41,7 @@ keycloak:
   postgresql:
       image:
         repository: postgres
-        tag: 13.16
+        tag: 13.18
       existingSecret: "keycloak-postgresql"
       postgresqlDataDir: /data/pgdata
       persistence: