windows: fix list type in legacy module utils (#30483)

* windows: fix list type in legacy module utils

* only change the return for the list type instead of affecting it all

* additional null check when using an array

test/integration/targets/win_module_utils_legacy/library/testlist.ps1

@@ -0,0 +1,12 @@
+#powershell
+
+#Requires -Module Ansible.ModuleUtils.Legacy
+
+$params = Parse-Args $args
+$value = Get-AnsibleParam -Obj $params -Name value -Type list
+
+if ($value -isnot [array]) {
+    Fail-Json -obj @{} -message "value was not a list but was $($value.GetType().FullName)"
+}
+
+Exit-Json @{ count = $value.Count }