Fix JSONNET rendiner for alerts
diff --git a/roles/kube_prometheus_stack/files/jsonnet/rules.jsonnet b/roles/kube_prometheus_stack/files/jsonnet/rules.jsonnet
index 0eed9bd..7cef869 100644
--- a/roles/kube_prometheus_stack/files/jsonnet/rules.jsonnet
+++ b/roles/kube_prometheus_stack/files/jsonnet/rules.jsonnet
@@ -1,9 +1,7 @@
 local mixins = import 'mixins.libsonnet';
 
 {
-  [mixin]:
-    mixins[mixin].prometheusAlerts + (
-      if std.objectHasAll(mixins[mixin], 'prometheusRules') then mixins[mixin].prometheusRules else {}
-    )
-  for mixin in std.objectFields(mixins)
+  [mixin]: {
+    groups: (mixins[mixin].prometheusAlerts.groups + if std.objectHasAll(mixins[mixin], 'prometheusRules') then mixins[mixin].prometheusRules.groups else [])
+  } for mixin in std.objectFields(mixins)
 }