Read more reject messages from debug logs in feature_dersig.py

Summary:
Partial backport of Core PR14119
https://github.com/bitcoin/bitcoin/pull/14119/files#diff-a22114218da7fa06c1bcd16d75c29bc7

Depends on D3862

Reviewer note: Some parts of the test differ due to changes done in D521. I left out the forced single-threaded validation since it's no longer relevant.

Test Plan: test_runner.py feature_dersig

Reviewers: #bitcoin_abc, deadalnix, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D3875