refactor: Use member initializers in CCheckQueue
Summary:
This is a backport of core#18710 [1/4]
https://github.com/bitcoin/bitcoin/pull/18710/commits/0ef938685b5c079a6f5a98daf0e3865d718d817b
Test Plan: ninja all check-all
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D10985