[chronik] Consistently sync the validation queue in functional tests

Summary:
In several places in chronik tests, a peer send a block to the node and waits for the node to catch up before calling chronik. This is racy because it doesn't guarantee that the validation callbacks ran and chronik might not be synced yet. Fix this by consistently syncing the validation queue in these cases.
There are likely other similar edge cases but this should avoid most of the random (and rare) failures due to this race condition.

Test Plan:

./test/functional/test_runner.py chronik_*

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D17675