Update with flyctl switched to searching for images remotely

[jakelacey2012]

Below is an example of how I deploy preview branches, where I build a custom image and then use that, this was working but no longer does in the past couple of days, I think its because of the latest changes with flyctl, which cause images to use the remote image resolver rather than the local image resolver by default.

      - name: Build elixir image
        run: docker build -t custom-image-elixir:1.16 -f Dockerfile .

      - name: Deploy PR app to Fly.io

        id: deploy
        uses: superfly/[email protected]
        with:
          name: pr-${{ github.event.number }}-savvychef
          image: custom-image-elixir:1.16