Correct case of $IsMacOS special variable

test/powershell/Modules/Microsoft.PowerShell.Utility/New-Object.Tests.ps1

@@ -2,7 +2,7 @@
 # Licensed under the MIT License.
 Describe "New-Object" -Tags "CI" {
     It "Support 'ComObject' parameter on platforms" {
-        if ($IsLinux -or $IsMacOs ) {
+        if ($IsLinux -or $IsMacOS ) {
             { New-Object -ComObject "Shell.Application" } | Should -Throw -ErrorId "NamedParameterNotFound,Microsoft.PowerShell.Commands.NewObjectCommand"
         } else {
             # It works on NanoServer and IoT too

test/powershell/engine/Basic/Assembly.LoadNative.Tests.ps1

@@ -23,7 +23,7 @@ Describe "Can load a native assembly" -Tags "CI" {
             $arch = "linux-" + $processArch
             $nativeDllName = "nativedll.so"
             $sourceDllName = "libhostpolicy.so"
-        } elseif ($IsMacOs) {
+        } elseif ($IsMacOS) {
             $arch = "osx-" + $processArch
             $nativeDllName = "nativedll.dylib"
             $sourceDllName = "libhostpolicy.dylib"