Add syntax check for pull requests

.github/workflows/update-dns.yaml

@@ -8,7 +8,12 @@ on:
       - 'zonefiles/**.zone'
 
 jobs:
+  validate-zonefiles:
+    uses: ./.github/workflows/validate-zonefiles.yaml
+
   update-dns:
+    needs:
+      - validate-zonefiles
     runs-on: ubuntu-latest
     steps:
       - name: Check out code

.github/workflows/validate-zonefiles.yaml

@@ -0,0 +1,29 @@
+name: Validate zonefile syntax
+
+on:
+  pull_request:
+    paths:
+      - 'zonefiles/**.zone'
+  push:
+    branches-ignore:
+      - main
+    paths:
+      - 'zonefiles/**.zone'
+
+jobs:
+  named-checkzone:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v3
+        with:
+          fetch-depth: 2
+
+      - name: Verify zonefile syntax
+        run: |
+          set -e
+          for zonefile in zonefiles/*.zone; do
+            zone=${zonefile##*/}
+            zone=${zone%.zone}
+            named-checkzone "$zone" "$zonefile"
+          done