fix(test): Fix 'cache_path' test in Linux

Signed-off-by: Hsiao-nan Cheung <niheaven@gmail.com>

test/Scoop-Core.Tests.ps1

@@ -243,14 +243,14 @@ Describe 'cache_path' -Tag 'Scoop' {
         $ret = cache_path 'git' '2.44.0' $url
         $inputStream = [System.IO.MemoryStream]::new([System.Text.Encoding]::UTF8.GetBytes($url))
         $sha = (Get-FileHash -Algorithm SHA256 -InputStream $inputStream).Hash.ToLower().Substring(0, 7)
-        $ret | Should -Be "$cachedir\git#2.44.0#$sha.zip"
+        $ret | Should -Be (Join-Path $cachedir "git#2.44.0#$sha.zip")
     }
 
     # # NOTE: Remove this 6 months after the feature ships.
     It 'returns the old format cache path for a given input' {
         Mock Test-Path { $true }
         $ret = cache_path 'git' '2.44.0' 'https://example.com/git.zip'
-        $ret | Should -Be "$cachedir\git#2.44.0#https_example.com_git.zip"
+        $ret | Should -Be (Join-Path $cachedir 'git#2.44.0#https_example.com_git.zip')
     }
 }