Fix constructing PSModulePath if a sub-path has trailing separator (#13147)

* Fix constructing PSModulePath if a sub-path has trailing separator

* skip test on Linux

* Removed test as the system env var needs to be modified to repro

* Add test

* Fix test by comparing against incorrectly created path

* Update test to be cross platform

test/powershell/engine/Module/ModulePath.Tests.ps1

@@ -187,4 +187,18 @@ Describe "SxS Module Path Basic Tests" -tags "CI" {
             Remove-Item -Path $userConfigPath -Force
         }
     }
+
+    It 'User PSModulePath has trailing separator' {
+        if ($IsWindows) {
+            $validation = "*\$env:SystemDrive\*"
+        }
+        else {
+            $validation = "*//*"
+        }
+
+        $newUserPath = Join-Path $expectedUserPath ([System.IO.Path]::DirectorySeparatorChar)
+        $env:PSModulePath = $env:PSModulePath.Replace($expectedUserPath, $newUserPath).Replace($expectedSharedPath,"")
+        $out = & $powershell -noprofile -command '$env:PSModulePath'
+        $out.Split([System.IO.Path]::PathSeparator, [System.StringSplitOptions]::RemoveEmptyEntries) | Should -Not -BeLike $validation
+    }
 }