fix(tests): move Pester pin to 6.0.1 and allow empty -ForEach collections

The GitHub-hosted runner images now ship Pester 6.0.1. PSDepend imports the
pinned Pester, then PowerShellBuild's Test-PSBuildPester runs
`Import-Module Pester -MinimumVersion 5.0.0`, which resolves to the highest
installed version and collides with the already-loaded 5.7.1 DLL.

Bumping the pin exposes a second, quieter problem. Pester 6 throws on a
null/empty -ForEach by default (Run.FailOnNullOrEmptyForEach); Pester 5
quietly generated zero tests. The throw happens during discovery, so Pester
fails the entire container (the whole file). A failed container does not
increment FailedCount, and Test-PSBuildPester only throws on FailedCount --
so the build passes while that file's tests never run.

The affected collections are legitimately empty in a default module:
  - $helpLinks           -- a command declares no http(s) .LINK
  - $commandParameters   -- a command declares only common parameters
  - $helpParameterNames  -- likewise
  - $dependencies        -- RequiredModules is commented out (template default)

$commands is deliberately left strict: an empty command list means the module
failed to import and should fail loudly.

Verified by rendering the template with Initialize-Template.ps1 and running
./build.ps1 -Task Test under Pester 6.0.1:

  before  Tests Passed: 27, containers failed: 2 (Help.tests.ps1, Manifest.tests.ps1)
  after   Tests Passed: 30, containers failed: 0

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015fsEPNYeL5LKdWLDNdv3T6

Author: tablackburn

build.depend.psd1

@@ -8,7 +8,7 @@
         }
     }
     'Pester'           = @{
-        Version    = '5.7.1'
+        Version    = '6.0.1'
         Parameters = @{
             SkipPublisherCheck = $true
         }

tests/Help.tests.ps1

@@ -161,7 +161,7 @@ Describe "Test help for <_.Name>" -ForEach $commands {
         ($commandHelp.Examples.Example.Remarks | Select-Object -First 1).Text | Should -Not -BeNullOrEmpty
     }
 
-    It 'Help link <_> is valid' -ForEach $helpLinks {
+    It 'Help link <_> is valid' -ForEach $helpLinks -AllowNullOrEmptyForEach {
         $currentProgressPreference = $ProgressPreference
         $ProgressPreference = 'SilentlyContinue'
         $invokeWebRequestParameters = @{
@@ -175,7 +175,7 @@ Describe "Test help for <_.Name>" -ForEach $commands {
         $statusCode | Should -Be '200'
     }
 
-    Context 'Parameter <_.Name>' -Foreach $commandParameters {
+    Context 'Parameter <_.Name>' -Foreach $commandParameters -AllowNullOrEmptyForEach {
 
         BeforeAll {
             $parameter         = $_
@@ -220,7 +220,7 @@ Describe "Test help for <_.Name>" -ForEach $commands {
         }
     }
 
-    Context 'Test <_> help parameter help for <commandName>' -Foreach $helpParameterNames {
+    Context 'Test <_> help parameter help for <commandName>' -Foreach $helpParameterNames -AllowNullOrEmptyForEach {
 
         # Shouldn't find extra parameters in help
         It 'finds help parameter in code: <_>' {

tests/Manifest.tests.ps1

@@ -208,7 +208,7 @@ Describe 'Module manifest' {
             $changelogVersion -as [Version] | Should -Be ( $manifestData.Version -as [Version] )
         }
 
-        Context 'Module Dependency' -ForEach $dependencies {
+        Context 'Module Dependency' -ForEach $dependencies -AllowNullOrEmptyForEach {
             # This ensures we keep our dependent modules in sync between the manifest file and the requirements
             # script used to bootstrap and test.
             BeforeAll {