[backport#16542 3/4] Check error messages in descriptor tests

Summary:
https://github.com/bitcoin/bitcoin/pull/16542/commits/6e1ae58298bc0069b95dfcd531c493a3825bded7

Depends on D6643

Partial backport of Core PR16542

Test Plan:

ninja check

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D6648