change code cov pool (#6647)

Author: michaelgsharp

build/codecoverage-ci.yml

@@ -15,4 +15,5 @@ jobs:
         _targetFramework: net6.0
     codeCoverage: true
     pool:
-      vmImage: windows-2019
+      name: NetCore-Public
+      demands: ImageOverride -equals 1es-windows-2019-open