(maint) Add Pester to Packages Manifest

Add pester package so its downloaded and available for Validation step.

This means the validation step can be used in a fully offline environment.

packages/chocolatey.json

@@ -25,6 +25,7 @@
         { "name": "KB3063858", "internalize": false },
         { "name": "microsoft-edge" },
         { "name": "nexus-repository" },
+        { "name": "pester" },
         { "name": "sql-server-express" },
         { "name": "temurin21jre" },
         { "name": "vcredist140" }