Build SourceIndex on VS2026 (#65212)

Author: wtgodbe

.azure/pipelines/ci.yml

@@ -715,7 +715,7 @@ extends:
                 versionSpec: 20.x
             pool:
               name: $(DncEngInternalBuildPool)
-              demands: ImageOverride -equals 1es-windows-2022
+              demands: ImageOverride -equals windows.vs2026preview.scout.amd64
 
       # Publish to the BAR and perform source indexing. Wait until everything else is done.
       - ${{ if notin(variables['Build.Reason'], 'PullRequest') }}: