ci: skip docker-image when DockerHub secrets are missing

Author: furedericca-lab

.github/workflows/docker-image.yml

@@ -12,6 +12,7 @@ env:
 
 jobs:
   docker_amd64:
+    if: ${{ secrets.DOCKERHUB_USERNAME != '' && secrets.DOCKERHUB_TOKEN != '' }}
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -43,6 +44,7 @@ jobs:
             ${{ env.DOCKERHUB_REPO }}:${{ env.VERSION }}-amd64
 
   docker_arm64:
+    if: ${{ secrets.DOCKERHUB_USERNAME != '' && secrets.DOCKERHUB_TOKEN != '' }}
     runs-on: ubuntu-24.04-arm
     steps:
       - name: Checkout
@@ -74,6 +76,7 @@ jobs:
             ${{ env.DOCKERHUB_REPO }}:${{ env.VERSION }}-arm64
 
   docker_manifest:
+    if: ${{ secrets.DOCKERHUB_USERNAME != '' && secrets.DOCKERHUB_TOKEN != '' }}
     runs-on: ubuntu-latest
     needs:
       - docker_amd64