Use for-loop instead of list comprehension

Summary:
To make it clear that we are intentionally using it for its
side-effects.

Backport 1-of-6 for Core PR10781

Test Plan: test_runner.py p2p-compactblocks

Reviewers: deadalnix, schancel, Fabien, #bitcoin_abc

Reviewed By: Fabien

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1998