validation: CVerifyDB::VerifyDB: Use locking annotation

Summary:
instead of recursively locking unconditionally

This concludes backport of core#21055 [16/16]
https://github.com/bitcoin/bitcoin/pull/21055/commits/e11b6496506246882df450586acf735dabedf731

Depends on D11221

Test Plan:
With debug and clang:

ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11222