mail/roundcube-thunderbird_labels: Update to 1.6.0
ChangeLog:
https://github.com/mike-kfed/roundcube-thunderbird_labels/blob/v1.6.0/Changelog
PR: 266986
MFH: 2022Q4
Security: 127674c6-4a27-11ed-9f93-002b67dfc673
(cherry picked from commit c0435e8ba6dd5219714f33854af06b8b5e02604d)