Search for duplicates only among already migrated issues

Author: ViliusS

src/githubHelper.ts

@@ -158,6 +158,7 @@ export class GithubHelper {
         owner: this.githubOwner,
         repo: this.githubRepo,
         state: 'all',
+        labels: 'gitlab merge request',
         per_page: perPage,
         page: page,
       });