test: Rename wait until helper to wait_until_helper
Summary:
This is a backport of core#19816 [1/2]
https://github.com/bitcoin/bitcoin/pull/19816/commits/fad2794e93b4f5976e81793a4a63aa03a2c8c686
Test Plan: ninja check-functional-extended
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D10168