Retry docker build in Forgejo workflow for transient pulls

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

@@ -11,7 +11,17 @@ jobs:
     runs-on: nix-host
     steps:
       - name: Build local image on runner host
-        run: docker build --pull -t lightscale-admin:local "https://git.centraworks.net/centra/lightscale-admin.git#${GITHUB_SHA}"
+        run: |
+          set -euo pipefail
+          for i in 1 2 3; do
+            if docker build --pull -t lightscale-admin:local "https://git.centraworks.net/centra/lightscale-admin.git#${GITHUB_SHA}"; then
+              exit 0
+            fi
+            if [ "$i" -lt 3 ]; then
+              sleep 10
+            fi
+          done
+          exit 1
 
       - name: Show built image
         run: docker image ls lightscale-admin:local