ci: migrate controller tests to Pester 6 (#6)

## Summary

- Pin the controller CI dependency to Pester 6.2.0.
- Require Pester 6.2.0 through 6.x for controller tests.
- Preserve controller logic, fixtures, and workflow behavior.

Refs AtlassianPS/AtlassianPS#12

## Validation

- Pester 5.7.1 baseline: 6 passed, 0 failed, 0 skipped, 0 failed blocks,
0 failed containers.
- Pester 6.2.0: 6 passed, 0 failed, 0 skipped, 0 failed blocks, 0 failed
containers.
- Invoke-ScriptAnalyzer dependency-updates -Recurse -Severity
Warning,Error -EnableExit passed with PSScriptAnalyzer 1.25.0.
- actionlint 1.7.12 passed against all workflows.
- git diff --check passed.
- Independent review found no issues.

Test-count change: none.

Author: lipkau

.github/workflows/ci.yml

@@ -26,7 +26,7 @@ jobs:
         shell: pwsh
         run: |
           Set-PSRepository -Name PSGallery -InstallationPolicy Trusted
-          Install-Module Pester -RequiredVersion 5.7.1 -Scope CurrentUser -Force
+          Install-Module Pester -RequiredVersion 6.2.0 -Scope CurrentUser -Force
           Install-Module PSScriptAnalyzer -RequiredVersion 1.25.0 -Scope CurrentUser -Force
 
       - name: Analyze controller

dependency-updates/Tests/Update-RepositoryDependencies.Tests.ps1

@@ -1,4 +1,4 @@
-#requires -Modules @{ ModuleName = 'Pester'; ModuleVersion = '5.7'; MaximumVersion = '5.999' }
+#requires -Modules @{ ModuleName = 'Pester'; ModuleVersion = '6.2.0'; MaximumVersion = '6.999' }
 
 BeforeAll {
     $scriptPath = Join-Path $PSScriptRoot '../Update-RepositoryDependencies.ps1'