Make copy-railpack-frontend-image job use Railpack version from Railpack builder Dockerfile

Author: FluxCapacitor2

.github/workflows/copy-railpack-frontend-image.yml

@@ -2,18 +2,27 @@ on:
   workflow_dispatch:
   push:
     branches: [main]
-    paths: [.github/workflows/copy-railpack-frontend-image.yml]
+    paths:
+      - .github/workflows/copy-railpack-frontend-image.yml
+      - builders/railpack/Dockerfile
 jobs:
   push_to_registry:
     runs-on: ubuntu-latest
     name: Copy railpack-frontend image to private registry
     steps:
+      - name: Checkout files
+        uses: actions/checkout@v6
+        with:
+          sparse-checkout: |
+            builders/railpack/
+
       - name: Log in to container registry
         run: docker login -u '${{ secrets.DOCKER_USERNAME }}' -p '${{ secrets.DOCKER_PASSWORD }}' registry.anvil.rcac.purdue.edu
 
       - name: Pull, tag, and push the image
         run: |
-          TAG=$(docker pull -q ghcr.io/railwayapp/railpack-frontend:v0.15.2)
+          VERSION=$(cat builders/railpack/Dockerfile | grep "RAILPACK_VERSION=" | cut -d= -f 2)
+          TAG=$(docker pull -q ghcr.io/railwayapp/railpack-frontend:v$VERSION)
           NEW_TAG=registry.anvil.rcac.purdue.edu/anvilops/railpack-frontend:latest
           docker tag $TAG $NEW_TAG
           docker push $NEW_TAG