fix link to trac issues

Since the project was archived, the group wasn't showing issues...

tsa/howto/gitlab.md

@@ -179,7 +179,7 @@ The issues and wiki of the "Tor" project are migrated. There are no
 other projects in Trac.
 
  * Trac wiki: <https://gitlab.torproject.org/legacy/trac>
- * Trac issues: <https://gitlab.torproject.org/groups/legacy/-/issues>
+ * Trac issues: <https://gitlab.torproject.org/legacy/trac/-/issues>
 
 Trac issues that remain are really legacy issues, others issues have
 been "moved" to the respective projects. @ahf, who did the migration,