Unit test sporadically fails when run in parallel

[panicgh]

v2.4.0 introduced a new unit tests, which requires tests to be run sequentially. It would be nice if unit tests were executable in parallel to save time (e.g. during packaging, rebuilding).

The "offending" test is spy_topics_tests.no_callback_called_if_no_write:
https://github.com/eProsima/Fast-DDS-statistics-backend/blob/v2.4.0/test/unittest/StatisticsBackend/SpyTopicsTests.cpp#L229

The test creates a monitor without publisher and so it checks that it indeed receives no samples. However, when tests run in parallel, another test may publish on the same DDS domain and interfere with the test. For example tests in my setup are run via /usr/bin/ctest --test-dir redhat-linux-build --output-on-failure --force-new-ctest-process -j12. Maybe the test can be made to use a different (quiet) DDS domain or there is a different solution.