These tests cannot (easily) be under "shared/nm-libnm-core-aux/tests"
because libnm/libnm-core requires code under shared while
"nm-libnm-core-aux" requires libnm/libnm-core. With autotools that is
not problem, but with meson we include sub directories in a particular
order and there is no way to foward declare stuff (AFAIK). To avoid
the circular dependency, add the tests to "clients/common/tests", which
is always built last.