test: style changes for p2p_blockfilters

Summary:
This is a backport of core#22311 [1&2/4]
https://github.com/bitcoin/bitcoin/pull/22311/commits/facd97ae0f0d816107aa3bc9de321244200636a0
https://github.com/bitcoin/bitcoin/pull/22311/commits/fa1668bf5084a190b26b022b9e625a7be3defa6e

Test Plan: test/functional/test_runner.py p2p_blockfilters

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11444