Fix Install-XHarness - attempt 2

Author: jpnurmi

scripts/device-test-utils.ps1

@@ -1,7 +1,8 @@
 function Install-XHarness {
     if (!(Get-Command xharness -ErrorAction SilentlyContinue))
     {
-        Push-Location (Test-Path env:CI ? $env:RUNNER_TEMP : $IsWindows ? $env:TMP : $IsMacos ? $env:TMPDIR : '/tmp')
+        $CI = Test-Path env:CI
+        Push-Location ($CI ? $env:RUNNER_TEMP : $IsWindows ? $env:TMP : $IsMacos ? $env:TMPDIR : '/tmp')
         dotnet tool install Microsoft.DotNet.XHarness.CLI --global --version '10.0.0-prerelease.25466.1' `
             --add-source https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-eng/nuget/v3/index.json
         Pop-Location