Add comment to explain the third_party_repo check

tests/applications/gnome-initial-setup/gnome_initial_setup_post.pm

@@ -66,9 +66,9 @@ sub run {
     assert_script_run("id $user");
     die("The expected password: $password is not valid for user $user.") if (assert_password($user, $password) != 0);
 
-
     # Check that third party repositories have been enabled.
     assert_script_run(q{fedora-third-party query | grep enabled}, timeout => 60);
+    # Verify that at least one third-party repository is configured (output is not empty)
     assert_script_run(q{fedora-third-party list --csv --columns=name,type | grep -q .});
 
     # Optional extra proof on the DNF side: