Switch Docker registry from custom to GitHub Container Registry in workflow.

Author: george-mcintyre

.github/workflows/docker-pub-epics-base.yml

@@ -18,7 +18,7 @@ jobs:
       - name: Login to Docker Hub
         uses: docker/login-action@v3
         with:
-          registry: ${{ env.REGISTRY }}
+          registry: ghcr.io
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
       - name: Checkout PVXS repo for Dockerfile
@@ -52,6 +52,6 @@ jobs:
           platforms: linux/amd64,linux/arm64
           push: true
           build-args: |
-            DOCKER_REGISTRY=${{ env.REGISTRY }}
+            DOCKER_REGISTRY=ghcr.io
             DOCKER_USERNAME=slac-epics
-          tags: ${{ env.REGISTRY }}/slac-epics/epics-base:latest
+          tags: ghcr.io/slac-epics/epics-base:latest