ci: migrate to action/ org composite actions

.gitea/workflows/main.yaml

@@ -1,16 +1,12 @@
-name: Synthetic CoreDNS Plugin CI/CD Build
+name: dns/synthetic build test
 on:
   push:
-    branches:
-      - main
+    branches: [main]
 jobs:
   test:
     runs-on: fritzlab
     steps:
-      - name: Check out repository code
-        uses: actions/checkout@v4
-      - name: run tests
-        run: |
-          set -x
-          docker build  \
-            --progress plain .
+      - uses: actions/checkout@v4
+      - uses: https://code.fritzlab.net/action/image-build@v1
+        with:
+          image: code.fritzlab.net/dns/synthetic

.gitea/workflows/pr.yaml

@@ -0,0 +1,12 @@
+name: dns/synthetic PR validation
+on:
+  pull_request:
+    branches: [main]
+jobs:
+  validate:
+    runs-on: fritzlab
+    steps:
+      - uses: actions/checkout@v4
+      - uses: https://code.fritzlab.net/action/image-build@v1
+        with:
+          image: code.fritzlab.net/dns/synthetic