check-sources: don't ignore toplevel in 3rd-party

We only want to ignore the files in the third-party subdirectories, not
the ones in the toplevel, that we write ourselves.

.bareos-check-sources-ignore

@@ -16,4 +16,4 @@ webui/public/css/*.min.*
 webui/public/css/bootstrap*.css.map
 systemtests/tests/bareos-basic/expected/status-subscriptions.txt
 systemtests/tests/bareos-basic/expected/status-subscriptions-detail.txt
-third-party/
+third-party/*/*