Update tests to account for when $PSHOME is readonly (#9279)

Co-Authored-By: SteveL-MSFT <slee@microsoft.com>


Co-authored-by: Travis Plunk <travis.plunk@microsoft.com>

test/powershell/Modules/Microsoft.PowerShell.Core/PSSessionConfiguration.Tests.ps1

@@ -1,12 +1,16 @@
 # Copyright (c) Microsoft Corporation. All rights reserved.
 # Licensed under the MIT License.
+
+Import-Module HelpersCommon
+
 try
 {
     # Skip all tests on non-windows and non-PowerShellCore and non-elevated platforms.
     $originalDefaultParameterValues = $PSDefaultParameterValues.Clone()
     $originalWarningPreference = $WarningPreference
     $WarningPreference = "SilentlyContinue"
-    $IsNotSkipped = ($IsWindows -and $IsCoreCLR -and (Test-IsElevated))
+    # Skip all tests if can't write to $PSHOME as Register-PSSessionConfiguration writes to $PSHOME
+    $IsNotSkipped = ($IsWindows -and $IsCoreCLR -and (Test-IsElevated) -and (Test-CanWriteToPsHome))
     $PSDefaultParameterValues["it:skip"] = !$IsNotSkipped
 
     #