/usr/share/debmake/extra3/package.cron.d.ex is in debmake 4.2.9-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | #
# Regular cron jobs for the @PACKAGE@ package
# See dh_installcron(1) and crontab(5).
#
0 4 * * * root [ -x /usr/bin/@PACKAGE@_maintenance ] && /usr/bin/@PACKAGE@_maintenance
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