Make workflow image name overrideable from Actions vars

Keep nikolaik/python-nodejs as the default image name in the workflow, but resolve it through a GitHub Actions variable so forks can publish to a different image without changing the repository.

Forks can set IMAGE_NAME in Actions variables or in workflow run configuration. That keeps the default behavior unchanged here while avoiding fork-specific edits in PRs.

Author: Wuodan

.github/workflows/build.yaml

@@ -6,6 +6,9 @@ on:
   schedule:
     - cron: "0 00,12 * * *"  # Twice a day
 
+env:
+  IMAGE_NAME: ${{ vars.IMAGE_NAME || 'nikolaik/python-nodejs' }}
+
 jobs:
   generate-matrix:
     name: Generate build matrix
@@ -59,12 +62,12 @@ jobs:
           context: .
           file: dockerfiles/${{ matrix.key }}.Dockerfile
           load: true
-          tags: nikolaik/python-nodejs:${{ matrix.key }}
+          tags: ${{ env.IMAGE_NAME }}:${{ matrix.key }}
 
       # Test
       - name: Run smoke tests
         run: |
-          docker run --rm nikolaik/python-nodejs:${{ matrix.key }} sh -c "node --version && npm --version && yarn --version && python --version && pip --version && pipenv --version && poetry --version && uv --version"
+          docker run --rm ${{ env.IMAGE_NAME }}:${{ matrix.key }} sh -c "node --version && npm --version && yarn --version && python --version && pip --version && pipenv --version && poetry --version && uv --version"
 
       # Push image
       - name: Push image
@@ -75,7 +78,7 @@ jobs:
           file: dockerfiles/${{ matrix.key }}.Dockerfile
           platforms: ${{ join(matrix.platforms) }}
           push: true
-          tags: nikolaik/python-nodejs:${{ matrix.key }}
+          tags: ${{ env.IMAGE_NAME }}:${{ matrix.key }}
 
       # Store build context
       - name: Add digest to build context