Run pull request validation once through native CI

.gitea/workflows/build-image.yml

@@ -2,11 +2,15 @@ name: build-image
 
 on:
   push:
-    branches: [main]
+    branches:
+    - main
+  pull_request:
+    branches:
+    - main
 
 jobs:
   docker:
-    runs-on: ubuntu-latest
+    runs-on: butler-ci
     steps:
       - uses: actions/checkout@v4
       - name: Select relevant delivery work
@@ -21,4 +25,5 @@ jobs:
           bash scripts/ci-select.sh
       - name: Build image
         if: ${{ steps.delivery.outputs.run == 'true' }}
-        run: make docker-build IMAGE_TAG=${{ gitea.sha }}
+        run: |
+          make ci-fast IMAGE_TAG=${{ gitea.sha }}