Update the Compliance job to checkout modified files in a PR run (Azure#35835)

Update the Compliance job to checkout modified files in a PR run

Author: alzimmermsft

eng/pipelines/templates/jobs/ci.yml

@@ -423,21 +423,29 @@ jobs:
               - '!sdk/**/test-recordings'
               - '!sdk/**/session-records'
 
-      - template: /eng/pipelines/templates/steps/generate-project-list-and-cache-maven-repository.yml
-        parameters:
-          Artifacts: ${{ parameters.Artifacts }}
-          AdditionalModules: ${{ parameters.AdditionalModules }}
-          JobType: 'Compliance'
-          UseCache: false
+      # For PullRequests CredScan will be run against the files changed in the PR.
+      # For non-pull requests CredScan
+      - ${{if eq(variables['Build.Reason'], 'PullRequest')}}:
+        - pwsh: |
+            $changedFiles = & "eng/common/scripts/get-changedfiles.ps1"
+            $tmp = ConvertTo-Json @($changedFiles | Sort-Object | Get-Unique) -Compress
+            Write-Host "##vso[task.setvariable variable=SparseCheckoutDirectories;]$tmp"
+      - ${{else}}:
+        - template: /eng/pipelines/templates/steps/generate-project-list-and-cache-maven-repository.yml
+          parameters:
+            Artifacts: ${{ parameters.Artifacts }}
+            AdditionalModules: ${{ parameters.AdditionalModules }}
+            JobType: 'Compliance'
+            UseCache: false
 
-      - task: PowerShell@2
-        displayName: Generate directories variable for sparse checkout
-        inputs:
-          pwsh: true
-          filePath: $(Build.SourcesDirectory)/eng/scripts/Generate-ServiceDirectories-From-Project-List.ps1
-          arguments: >
-            -SourcesDirectory $(Build.SourcesDirectory)
-            -ProjectList $(ProjectList)
+        - task: PowerShell@2
+          displayName: Generate directories variable for sparse checkout
+          inputs:
+            pwsh: true
+            filePath: $(Build.SourcesDirectory)/eng/scripts/Generate-ServiceDirectories-From-Project-List.ps1
+            arguments: >
+              -SourcesDirectory $(Build.SourcesDirectory)
+              -ProjectList $(ProjectList)
 
       # Skip sparse checkout for the `azure-sdk-for-<lang>-pr` private mirrored repositories
       # as we require the GitHub service connection to be loaded.