fix: dev: Fold receive_secure_serial into zone maintainance

Having two separate zone maintainance async jobs increases the risk of
race conditions. This commit folds the inline-signing resigning job
into the zone maintainance of the secure zone, ensuring only one async
job acts on a zone.

Closes #5816

Merge branch '5816-resign-single-source-of-truth' into 'main'

See merge request isc-projects/bind9!12005