Docker COPY fails Github actions with git lfs

I am using Github actions to build docker images with a file from git lfs.
I have the following step:

     - 
        name: Checkout code
        uses: actions/checkout@v2
        with:
          lfs: true
      - 
        run: head something.json

Which prints the data correctly.

When I run the same command from my dockerfile in the build stage,
I get the following lfs metadata:

#7 [4/5] RUN head something.json
#7 sha256:***
#7 0.138 version https://git-lfs.github.com/spec/v1
#7 0.138 oid sha256:***
#7 0.138 size 1230424
#7 DONE 0.2s

Dockerfile:

FROM bitnami/python:3.9.1

COPY . .

RUN head something.json

Action:

jobs:
  build-image:
    runs-on: ubuntu-latest
    steps:
      - 
        name: Checkout code
        uses: actions/checkout@v2
        with:
          lfs: true
      - 
        run: head something.json
      -
        name: Set up QEMU
        uses: docker/setup-qemu-action@v1
      -
        name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v1
      -
        name: Build and push
        id: docker_build
        uses: docker/build-push-action@v2
        with:
          push: true
          file: Dockerfile

Why the docker build takes the metadata and not the actual file?