Add bootstrap to global tool validation step

Author: adityapatwardhan

.pipelines/templates/release-validate-globaltools.yml

@@ -78,6 +78,9 @@ jobs:
     - pwsh: |
         $repoRoot = "$(Build.SourcesDirectory)/PowerShell"
 
+        Import-Module "$repoRoot/build.psm1" -Force -Verbose
+        Start-PSBootstrap -Scenario Dotnet
+
         $exeName = if ($IsWindows) { "pwsh.exe" } else { "pwsh" }
 
         $toolPath = "$(System.DefaultWorkingDirectory)/toolPath/${{ parameters.globalToolExeName }}"