Set multiple sparse checkout paths in one command/job (#841)

Co-authored-by: Ben Broderick Phillips <bebroder@microsoft.com>

eng/common/pipelines/templates/steps/sparse-checkout.yml

@@ -24,15 +24,13 @@ steps:
     - pwsh: |
         git clone --no-checkout --filter=tree:0 git://github.com/${{ repo.Name }} .
         git sparse-checkout init
-        git sparse-checkout set eng
+        $paths = ('${{ convertToJson(parameters.Paths) }}' | ConvertFrom-Json) -Join ' '
+        Invoke-Expression -Command "git sparse-checkout set eng $paths"
+        Write-Host "Set sparse checkout paths to:"
+        Get-Content .git/info/sparse-checkout
       displayName: Init sparse checkout ${{ repo.Name }}
       workingDirectory: ${{ coalesce(repo.WorkingDirectory, format('{0}/{1}', '$(System.DefaultWorkingDirectory)', repo.Name)) }}
 
-    - ${{ each path in parameters.Paths }}:
-      - pwsh: git sparse-checkout add ${{ path }}
-        displayName: Add sparse checkout path ${{ path }}
-        workingDirectory: ${{ coalesce(repo.WorkingDirectory, format('{0}/{1}', '$(System.DefaultWorkingDirectory)', repo.Name)) }}
-
     - pwsh: git checkout ${{ repo.Commitish }}
       displayName: Sparse checkout at ${{ repo.Commitish }}
       workingDirectory: ${{ coalesce(repo.WorkingDirectory, format('{0}/{1}', '$(System.DefaultWorkingDirectory)', repo.Name)) }}