chore: refer to var

Author: samrose

.github/workflows/test.yml

@@ -75,7 +75,7 @@ jobs:
         with:
           load: true
           context: .
-          file: "Dockerfile-{{ matrix.postgres_version }}"
+          file: "Dockerfile-${{ matrix.postgres_version }}"
           target: production
           build-args: |
             ${{ steps.args.outputs.result }}