Do not overwrite existing labels on auto generated dependency upgrade… (#20953)

* Do not overwrite existing labels on auto generated dependency upgrade issue

eng/scripts/check-external-dependency.ps1

@@ -57,6 +57,12 @@ function Set-GitHubIssue($Package) {
   $issue = Get-GithubIssue -IssueTitle $issueTitle
   if ($issue) {
     if ($issue.body -ne $issueDesc) {
+      # Copy over current labels to avoid removing manually tagged labels
+      foreach($lbl in $issue.labels)
+      {
+        $labels += ",$($lbl.name)"
+      }
+      Write-Host "Updating existing issue  $($issue.number). Labels: $($labels)"
       $oldIssue = Update-GitHubIssue -RepoOwner $RepoOwner -RepoName $RepoName -AuthToken $AuthToken -IssueNumber $issue.number -Body $issueDesc -Labels $labels
       Write-Host "Updated existing issue $($oldIssue.number)"
     }