It turns out that Boost assertions are thread-unsafe,
(and can't be used from multiple threads concurrently).
This causes the test to fail with cryptic log corruptions sometimes.
Fix that by switching to thread-safe checks.
Fixesscylladb/scylladb#24982Closesscylladb/scylladb#26472
It seems that tests in test/boost/combined_tests have to define a test
suite name, otherwise they aren't picked up by test.py.
Fixes#24199Closesscylladb/scylladb#24200
