Using job matrix with uses tag fails

This is my workflow file:

on: [push, pull_request]

jobs:
    build_simppru_job:
        runs-on: ubuntu-latest
        name: This will test simppru on amd64 machine
        steps: 
            - name: Checkout
              uses: actions/checkout@v2
            - name: preconfig
              run: sudo docker run --rm --privileged multiarch/qemu-user-static --reset -p yes
            - name: test inside docker arm32
              uses: ./.github/action_test_amd64
            - name: postconfig
              run: ls build -l

On running it fails with the following error:

Error: .github#L1
the `uses' attribute must be a path, a Docker image, or owner/repo@ref

Repository: simpPRU/.github at master · VedantParanjape/simpPRU · GitHub

There’s no action.yaml or action.yml file in the .github/action_test_amd64/ directory of your repository, not it can’t be a valid action for uses. If you want to use the Dockerfile and entrypoint.sh script there to make a custom Docker action, see Creating a Docker container action - GitHub Docs for what you need to do.

I somehow seem to copy the wrong action file. I was doing the following:

matrix:
    arch: ["./arm", "./amd64"]
....
....
uses: ${{ matrix.arch }}