change machine type to one available in central region

.github/workflows/zcashd-cd.yml

@@ -11,7 +11,6 @@ on:
 env:
   PROJECT_ID: zealous-zebra
   REGION: us-central1
-  ZONE: us-central1-c
 
 jobs:
 
@@ -44,7 +43,7 @@ jobs:
           --boot-disk-size 100GB \
           --container-image "electriccoinco/zcashd" \
           --container-env ZCASHD_NETWORK="${{ github.event.inputs.network }}" \
-          --machine-type n2d-standard-4 \
+          --machine-type n2-standard-4 \
           --service-account cos-vm@zealous-zebra.iam.gserviceaccount.com \
           --scopes cloud-platform \
           --tags zcashd \