Switch PATH setting to new environment files

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

.github/workflows/build.yml

@@ -28,7 +28,7 @@ jobs:
     - name: Install Rustup (macOS)
       run: |
         curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
-        echo ::add-path::$HOME/.cargo/bin
+        echo "$HOME/.cargo/bin" >> $GITHUB_PATH
       if: runner.os == 'macOS'
 
     - name: Set Rustup profile to minimal
@@ -83,7 +83,7 @@ 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