azure-pipelines.yml: Updated to use vso[build.updatebuildnumber] rather than vso[task.setvariable variable=Build.BuildNumber], since updating system variables is no longer supported

Author: NightOwl888

azure-pipelines.yml

@@ -157,7 +157,7 @@ stages:
     - powershell: |
         $version = Get-Content '$(Build.ArtifactStagingDirectory)/$(VersionArtifactName)/$(PackageVersionFileName)' -Raw
         Write-Host "##vso[task.setvariable variable=PackageVersion;]$version"
-        Write-Host "##vso[task.setvariable variable=Build.BuildNumber;]$version"
+        Write-Host "##vso[build.updatebuildnumber]$version"
       displayName: 'Read PackageVersion from File to Build.BuildNumber'
 
     - template: 'build/azure-templates/show-all-environment-variables.yml'