longhorn: pin vault sync to rpi workers

infrastructure/longhorn/core/vault-sync-deployment.yaml

@@ -15,6 +15,17 @@ spec:
         app: longhorn-vault-sync
     spec:
       serviceAccountName: longhorn-vault-sync
+      nodeSelector:
+        node-role.kubernetes.io/worker: "true"
+      affinity:
+        nodeAffinity:
+          preferredDuringSchedulingIgnoredDuringExecution:
+            - weight: 80
+              preference:
+                matchExpressions:
+                  - key: hardware
+                    operator: In
+                    values: ["rpi5", "rpi4"]
       containers:
         - name: sync
           image: alpine:3.20