Tests: fix ignored return value from htmlproofer
Tests: fix ignored return value from htmlproofer

Fixes bug in the tests introduced in
0e7d61a91452d7a30577831a118873355514e593

bitcoin-core/bitcoincore.org,bitcoin-core/bitcoincore.org,bitcoin-core/bitcoincore.org,bitcoin-core/bitcoincore.org,bitcoin-core/bitcoincore.org,bitcoin-core/bitcoincore.org