Fix ninja check with TEST_WITH_UPGRADE_ACTIVATED for newer versions of boost

Summary:
Without this patch, ninja check on upgrade-activated unit tests will fail
because the behavior subtly changed to require a -- between BOOST test module arguments
and custom arguments. Versions of boost > 1.58 fail.

Earliest documentation I could find that references this behavior: https://www.boost.org/doc/libs/1_70_0/libs/test/doc/html/boost_test/runtime_config/custom_command_line_arguments.html

Test Plan:
Passes on machines for both versions of BOOST 1.58 and 1.62 (fails without this patch):

cmake -GNinja -DTEST_WITH_UPGRADE_ACTIVATED=ON ..
ninja check

Reviewers: #bitcoin_abc, deadalnix, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D4647