test: Add missing signal.h header
test: Add missing signal.h header

util_tests.cpp needs to include the signal.h header on FreeBSD.

Reported by denis2342 on IRC.

Github-Pull: #12447
Rebased-From: dd7e42cbb4390788705031ffa0bc893d26f0597e
Tree-SHA512: 10ead029bb59f5d69e37b5679c710f22d64051de26e1ec8342eec4e4dec4d76249e16dff78d192972bcb8d139d99c7555a7cb2fe43b2b911103eab6d6f943b79

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