Roll back windows images used in testing to Windows Server 2019 (#16958)

.vsts-ci/templates/windows-test.yml

@@ -1,5 +1,5 @@
 parameters:
-  pool: 'windows-latest'
+  pool: 'windows-2019'
   parentJobs: []
   purpose: ''
   tagSet: 'CI'

.vsts-ci/windows-daily.yml

@@ -53,7 +53,7 @@ stages:
   jobs:
   - job: win_test
     pool:
-      vmImage: windows-latest
+      vmImage: windows-2019
     displayName: Windows Test
     timeoutInMinutes: 90