ci: fix path to Dockerfile

.github/workflows/build_and_push_docker_images.yaml

@@ -169,4 +169,4 @@ jobs:
         build-args: |
           EMQX_NAME=${{ matrix.profile }}${{ steps.pre-meta.outputs.img_suffix }}
           EXTRA_DEPS=${{ steps.pre-meta.outputs.extra_deps }}
-        file: source/${{ matrix.os[2] }}
+        file: ${{ matrix.os[2] }}