build: more accurate dependencies on Boost libraries

See also named-data/ndn-cxx@5686c51b87b6a642aa2dc8d93e061caebbb226cc

Change-Id: I9da751fe934558c753eeac0b93d7a4d505e4eb91
diff --git a/tests/wscript b/tests/wscript
index 55295bd..499d754 100644
--- a/tests/wscript
+++ b/tests/wscript
@@ -8,7 +8,7 @@
         target=f'{top}/unit-tests',
         name='unit-tests',
         source=bld.path.ant_glob(['*.cpp', 'unit-tests/**/*.cpp']),
-        use='libndn-cert',
+        use='BOOST_TESTS libndn-cert',
         defines=[tmpdir],
         includes=top,
         install_path=None)