Update GitRepository Receiver, and Kustomization to v1

Signed-off-by: Somtochi Onyekwere <somtochionyekwere@gmail.com>

cmd/flux/testdata/export/receiver.yaml

@@ -1,5 +1,5 @@
 ---
-apiVersion: notification.toolkit.fluxcd.io/v1beta2
+apiVersion: notification.toolkit.fluxcd.io/v1
 kind: Receiver
 metadata:
   name: flux-system
@@ -8,6 +8,7 @@ spec:
   events:
   - ping
   - push
+  interval: 10m0s
   resources:
   - kind: GitRepository
     name: flux-system