[backport#19022] test: Fix intermittent failure in feature_dbcrash

Summary:
test: Fix intermittent failure in feature_dbcrash (MarcoFalke)

Pull request description:

Example backtrace https://cirrus-ci.com/task/6005716207009792?command=functional_test#L817

Backport of Core PR19022

Test Plan:

ninja
test_runner.py feature_dbcrash

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7406