[chronik] Wait for the correct tip finalization in chronik_ws_ordering

Summary: The test correctly waits for the last block to get finalized in order to check message ordering, but it's wrong on the tip because the get_quorum function actually mines blocks.

Test Plan:

./test/functional/test_runner.py chronik_ws_ordering

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D16194