Bug#965481: ddclient: Removal of obsolete debhelper compat 5 and 6 in bookworm

[Richard Hansen]

Changes for debhelper-compat 12 have already been committed:
https://salsa.debian.org/debian/ddclient/-/blob/c85aa96a6b51386e2f7994fc1ad7ae60f9cda098/debian/control#L5
but I'm waiting for a sponsor to upload:
https://bugs.debian.org/962159