[backport#14771]test: Add BOOST_REQUIRE to getters returning optional

Summary:
https://github.com/bitcoin/bitcoin/pull/14771/commits/fa21ca09a807e18476babe2651ad62df6477bbf0

Backport of Core PR14771

Test Plan:

ninja check check-functional

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D7278