Use correct leading slash in common.ps1 repo root resolution (#10694)

* Use correct leading slash in common.ps1 repo root resolution

* Update eng/common/scripts/common.ps1

Co-authored-by: Wes Haggard <weshaggard@users.noreply.github.com>

---------

Co-authored-by: Wes Haggard <weshaggard@users.noreply.github.com>

Author: benbp

eng/common/scripts/common.ps1

@@ -1,6 +1,6 @@
 # cSpell:ignore Apireview
 # cSpell:ignore Onboarded
-$RepoRoot = Resolve-Path "${PSScriptRoot}..\..\..\.."
+$RepoRoot = Resolve-Path (Join-Path $PSScriptRoot .. .. ..)
 $EngDir = Join-Path $RepoRoot "eng"
 $EngCommonDir = Join-Path $EngDir "common"
 $EngCommonScriptsDir = Join-Path $EngCommonDir "scripts"