Fix gcc11 annonymous namespace warnings
This fixes warnings of the following type:
warning: 'MEPProvider' has a field 'MEPProvider::m_bad_mfps_sd' whose type uses the anonymous namespace [-Wsubobject-linkage]
where MEPProvider
is a Service
and m_bad_mfps_sd
is a Gaudi::Accumulators::Histogram<1, Gaudi::Accumulators::atomicity::full, float>
.