with-post-step: Only first cmd line read by windows

[IanButterworth]

While other platforms read multiple lines, Windows appears to only execute the first line entered

    - uses: pyTooling/Actions/with-post-step@v0.4.6
      with:
        main: |
          echo "main 1"
          echo "main 2"
        post: |
          echo "post 1"
          echo "post 2"
      env:
        GH_TOKEN: ${{ github.token }}

On Windows, only echo "main 1" and echo "post 1" will be executed

[Paebbels]

I'm open to accept pull requests.

Please also see #82.