fix: support new Dockerfile structure in PR builds

Author: smlx

.github/workflows/build.yaml

@@ -65,8 +65,10 @@ jobs:
         tags: ${{ steps.docker_metadata.outputs.tags }}
         labels: ${{ steps.docker_metadata.outputs.labels }}
         file: Dockerfile
-        build-args: BINARY=${{ matrix.binary }}
-        context: dist/${{ matrix.binary }}_linux_amd64_v1
+        build-args: |
+          BINARY=${{ matrix.binary }}
+          TARGETPLATFORM=${{ matrix.binary }}_linux_amd64_v1
+        context: dist
   check-tag:
     permissions:
       contents: read