Fetch source tarball directly in Forgejo workflow

.forgejo/workflows/build-local-image.yml

@@ -10,10 +10,15 @@ jobs:
   build:
     runs-on: nix-host
     steps:
+      - name: Fetch repository archive
+        run: |
+          set -euo pipefail
+          curl -fsSL "https://git.centraworks.net/api/v1/repos/centra/lightscale-admin/archive/${GITHUB_SHA}.tar.gz?rev=${GITHUB_SHA}" \
+            | tar -xz --strip-components=1
+
       - name: Validate workspace
         run: |
-          pwd
+          set -euo pipefail
-          ls -la
           test -f Dockerfile
 
       - name: Build local image on runner host