Fix Pester test reporter format mismatch

Change dorny/test-reporter from java-junit to dotnet-nunit to match
the NUnitXml format generated by Invoke-Tests.ps1

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: tpcarman

.github/workflows/Pester.yml

@@ -40,5 +40,5 @@ jobs:
         with:
           name: Pester Tests
           path: Tests/testResults.xml
-          reporter: java-junit
+          reporter: dotnet-nunit
           fail-on-error: true