tests: Add missing cs_main locks required when accessing pcoinsdbview, pcoinsTip or pblocktree

Summary:
This is a backport of Core PR15413

Depends on D4591

Test Plan:

make check
ninja bench-bitcoin

Ensure clang doesn't warnign about thread safety.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D4592