Update to pool-provider sourced machines (#894)

Author: vatsan-madhavan

azure-pipelines.yml

@@ -31,6 +31,8 @@ jobs:
   parameters:
     ${{ if and(ne(variables['System.TeamProject'], 'public'), notin(variables['Build.Reason'], 'PullRequest')) }}:
       # agent pool can't be read from a user-defined variable (Azure DevOps limitation)
-      agentPool: dotnet-internal-vs2019-preview
+      pool:
+        name: NetCoreInternal-Pool
+        queue: buildpool.windows.10.amd64.vs2019.pre
       # runAsPublic is used in expressions, which can't read from user-defined variables
       runAsPublic: false