Start-DbaMigration.Tests - Fix additional PS 5.1 .Count issues

Wrap $script:ssisCalls and Where-Object results in @() for PS 5.1
compatibility where .Count returns $null on single objects.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: potatoqualitee

tests/Start-DbaMigration.Tests.ps1

@@ -433,10 +433,10 @@ Describe $CommandName -Tag UnitTests {
 
                     $null = Start-DbaMigration -Source "sql1" -Destination "sql2" -Exclude $excludeForSsisOnly
                     $script:stopMessages | Should -BeNullOrEmpty
-                    $script:ssisCalls.Count | Should -Be 1
+                    @($script:ssisCalls).Count | Should -Be 1
                     $script:ssisCalls[0].Source.VersionMajor | Should -Be 15
                     $script:ssisCalls[0].Destination | Should -Be "sql2"
-                    ($script:messages | Where-Object { $PSItem -like "*Migrating SSIS catalog" }).Count | Should -Be 1
+                    @($script:messages | Where-Object { $PSItem -like "*Migrating SSIS catalog" }).Count | Should -Be 1
                 } finally {
                     foreach ($functionName in $functionNames) {
                         if ($originalFunctions.ContainsKey($functionName)) {