test: whitelist rpc_rawtransaction peers to speed up tests

Summary:
Backport of core#22447.

Speeds up the test by ~3x on my machine.
Sorry for the style, it's the original material.

Test Plan:

./test/functional/test_runner.py rpc_rawtransaction

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D9828