Revert modifications caused by Code's test run (#3993)

VS Code 1.67.0 and up now modify the local `package.json` file during
test run. Because we first run our tests in CI and then package our
extension, this modification gets saved into the extension package. We
need to check the file back out from Git after the test run.

Author: andyleejordan

Diff for: vscode-powershell.build.ps1

@@ -118,6 +118,8 @@ task Build Restore, {
 task Test -If (!($env:TF_BUILD -and $global:IsLinux)) Build, {
     Write-Host "`n### Running extension tests" -ForegroundColor Green
     exec { & npm run test }
+    # Reset the state of files modified by tests
+    exec { git checkout package.json test/.vscode/settings.json}
 }
 
 task TestEditorServices -If (Get-EditorServicesPath) {