Enable build.ps1 -warnAsError in at least one CI leg

`build.sh --warnaserror` is already enabled in another CI leg.

Author: jjonescz

azure-pipelines.yml

@@ -436,12 +436,12 @@ stages:
     steps:
       - template: eng/pipelines/checkout-windows-task.yml
 
-      - powershell: eng/build.ps1 -configuration Release -prepareMachine -ci -restore -binaryLogName Restore.binlog 
+      - powershell: eng/build.ps1 -configuration Release -prepareMachine -ci -restore -warnAsError -binaryLogName Restore.binlog 
         displayName: Restore
 
       # We additionally restore during the build because the Microsoft.DotNet.Build.Tasks.Feed package only restores when we pass `-publish`. See https://github.com/dotnet/arcade/blob/37ccfd66358af6a37a0ec385ec31d1d71bdd8723/src/Microsoft.DotNet.Arcade.Sdk/tools/Tools.proj#L61-L66
       # Passing `-publish` during the restore step above fails due to no items needing published.
-      - powershell: eng/build.ps1 -configuration Release -prepareMachine -ci -restore -build -pack -publish -sign -binaryLogName Build.binlog /p:DotnetPublishUsingPipelines=true /p:ContinuousIntegrationBuildCorrectness=true
+      - powershell: eng/build.ps1 -configuration Release -prepareMachine -ci -restore -build -pack -publish -sign -warnAsError -binaryLogName Build.binlog /p:DotnetPublishUsingPipelines=true /p:ContinuousIntegrationBuildCorrectness=true
         displayName: Build
 
       # While this task is not executed in the official build, this serves as a PR check for whether symbol exclusions