Update CI to be ECR-only

`PREFIX` is being defaulted, so there's no ECR-specific options for the
build, we just have to remove DockerHub auth and ensure ECR auth.

.github/workflows/ci.yml

@@ -73,38 +73,13 @@ jobs:
           curl --proto '=https' --tlsv1.2 -sSf \
             https://raw.githubusercontent.com/restyled-io/restyler/main/install | sudo sh
 
-      - uses: docker/login-action@v3
-        with:
-          username: ${{ secrets.DOCKERHUB_USERNAME }}
-          password: ${{ secrets.DOCKERHUB_PASSWORD }}
-
-        # Necessary if pushing, but best-effort if pulling (rate limits)
-        continue-on-error: ${{ github.ref_name != 'main' }}
-
-      # TODO: lint
-
-      - name: "Build, test, and push (if main) sha-tagged images"
-        run: >-
-          restylers
-          ${{ runner.debug && '--debug' || '' }}
-          --sha ${{ github.sha }}
-          --write tested.yaml
-          --no-pull
-          ${{ github.ref_name == 'main' && '--push' || '' }}
-          ${{ needs.changes.outputs.restylers }}
-
       - if: ${{ github.ref_name == 'main' }}
+        name: AWS Login
         uses: aws-actions/configure-aws-credentials@v4
         with:
           aws-region: ${{ vars.AWS_REGION }}
           role-to-assume: ${{ vars.AWS_ROLE }}
 
-      - if: ${{ github.ref_name == 'main' }}
-        id: ecr-login
-        uses: aws-actions/amazon-ecr-login@v2
-        with:
-          registry-type: public
-
       - if: ${{ github.ref_name == 'main' }}
         name: Create ECR repositories if necessary
         run: |
@@ -118,19 +93,22 @@ jobs:
           done
 
       - if: ${{ github.ref_name == 'main' }}
-        name: Mirror image to ECR
+        name: ECR Login
+        id: ecr-login
+        uses: aws-actions/amazon-ecr-login@v2
+        with:
+          registry-type: public
+
+      # TODO: lint
+
+      - name: Build, test, and push (if main)
         run: >-
           restylers
           ${{ runner.debug && '--debug' || '' }}
-          --sha ${{ github.sha }}
+          --write tested.yaml
           --no-pull
-          --no-test
-          --push
-          --prefix "$PREFIX"
+          ${{ github.ref_name == 'main' && '--push' || '' }}
           ${{ needs.changes.outputs.restylers }}
-        env:
-          # TODO: use restyled-io alias once available
-          PREFIX: ${{ steps.ecr-login.outputs.registry }}/${{ vars.AWS_ECR_NAMESPACE }}/
 
       - name: Build merged restylers.yaml
         run: |