Use new environment files for modifying PATH

See https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/

Author: phil-opp

.github/workflows/build.yml

@@ -67,7 +67,7 @@ jobs:
     - name: Install Scoop (Windows)
       run: |
         Invoke-Expression (New-Object System.Net.WebClient).DownloadString('https://get.scoop.sh')
-        echo ::add-path::$HOME\scoop\shims
+        echo "$HOME\scoop\shims" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
       if: runner.os == 'Windows'
       shell: pwsh
     - name: Install QEMU (Windows)