title: Upload Multiple (Parallel) Files to a Single Release
body: <p>I'm quite new to github actions. I already managed to build my C++ program using CMAKE for ubuntu-latest and windows-latest, now I'm having problems uploading it to a release.
  I'm using a strategy matrix, so the different OS jobs run in parallel.</p>
  <p>My goal is to upload build files to a single Release Tag in which each file will have a custom name based on OS platform.</p>
  <p>ex.:</p>
  <pre class="lang-sh prettyprint-override"><code>Release Tag: V0.2.0
        Files: main_0.2.0_windows.exe
               main_0.2.0_ubuntu
                        ...
               main_0.2.0_other-OS.ext
  </code></pre>
  <p>Can someone help me to do so? Below is my current workflow yml.</p>
  <p>** I already managed to upload single files to single release tags for ubuntu-latest. For windows-latest I got an error saying that the file to upload is not found :( .</p>
  <pre class="lang-yaml prettyprint-override"><code>name: CMake
  
  on:
    push:
      branches: [ master ]
    pull_request:
      branches: [ master ]
    workflow_dispatch:
      inputs:
        trigger:
          required: false
          default: 'workflow_dispatcher'
    
  env:
    # Customize the CMake build type here (Release, Debug, RelWithDebInfo, etc.)
    BUILD_TYPE: Release
    VERSION: 0.2.0
  
  jobs:
    build:
      strategy:
        matrix:
          platform: [ ubuntu-latest, windows-latest ]
          python-version: ['2.7', '3.6']
    
      # The CMake configure and build commands are platform agnostic and should work equally
      # well on Windows or Mac.  You can convert this to a matrix build if you need
      # cross-platform coverage.
      # See: https://docs.github.com/en/free-pro-team@latest/actions/learn-github-actions/managing-complex-workflows#using-a-build-matrix
      runs-on: ${{ matrix.platform }}
      
      steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-python@v2
        with:
          python-version: ${{ matrix.python-version }}
        
      - name: Upgrade pip &amp; setuptools
        run: python -m pip install --upgrade pip setuptools
        
      - name: Install matplotlib &amp; numpy
        run: python -m pip install matplotlib numpy 
        
      - name: Copy numpy core to include folder
        run: python ${{github.workspace}}/cp-numpy-core.py
        
      - name: Configure CMake
        # Configure CMake in a 'build' subdirectory. `CMAKE_BUILD_TYPE` is only required if you are using a single-configuration generator such as make.
        # See https://cmake.org/cmake/help/latest/variable/CMAKE_BUILD_TYPE.html?highlight=cmake_build_type
        run: cmake -B ${{github.workspace}}/build -DCMAKE_BUILD_TYPE=${{env.BUILD_TYPE}}
        
      - name: Build
        # Build your program with the given configuration
        run: cmake --build ${{github.workspace}}/build --config ${{env.BUILD_TYPE}} --target main
        
      - name: Test
        working-directory: ${{github.workspace}}/build
        # Execute tests defined by the CMake configuration.  
        # See https://cmake.org/cmake/help/latest/manual/ctest.1.html for more detail
        run: ctest -C ${{env.BUILD_TYPE}}
        
      - name: Rename Ubuntu Files
        if: ${{ matrix.platform == 'ubuntu-latest' }}
        run: mv ${{github.workspace}}/build/main ${{github.workspace}}/build/main_${{ env.VERSION }}_${{ matrix.platform }}_${{ matrix.python-version }}
      
      - name: Rename Windows Files
        if: ${{ matrix.platform == 'windows-latest' }}
        run: Ren &quot;${{github.workspace}}\build\${{ env.BUILD_TYPE }}\main.exe&quot; &quot;${{github.workspace}}\build\${{ env.BUILD_TYPE }}\main_${{ env.VERSION }}_${{ matrix.platform }}_${{ matrix.python-version }}.exe&quot;
        
      - name: Upload Artifacts
      - uses: &quot;marvinpinto/action-automatic-releases@latest&quot;
        with:
          repo_token: &quot;${{ secrets.GITHUB_TOKEN }}&quot;
          automatic_release_tag: &quot;${{ env.BUILD_TYPE }}${{ env.VERSION }}/${{ matrix.platform }}/Python${{ matrix.python-version }}&quot;
          prerelease: true
          title: &quot;${{ env.BUILD_TYPE }} V${{ env.VERSION }} - OS: ${{ matrix.platform }} - Python: ${{ matrix.python-version }}&quot;
          files: |
            ${{github.workspace}}/build/main_${{ env.VERSION }}_${{ matrix.platform }}_${{ matrix.python-version }}
            ${{github.workspace}}\build\${{ env.BUILD_TYPE }}\main_${{ env.VERSION }}_${{ matrix.platform }}_${{ matrix.python-version }}.exe
  
  </code></pre>
  <p>Best regards &amp; Keep coding!</p>