Fix a warning with GCC 13.1

Summary:
Fix another (see D14005) dropped return value.

There are still a couple more warnings but they seem to be false positives, so you need to build with -Wno-dangling-reference to see no warning at all with GCC 13.1.

Test Plan:
With GCC 13.1

ninja all check-all

Check they throw no warning anymore.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14006