get_nucleus_name() returns string_view to temporary object

from the CI output:

[ 62%] Building CXX object tests/media/CMakeFiles/testMedia.dir/testEnvironment.cpp.o
In file included from /builds/2/corsika/tests/stack/testHistoryStack.cpp:9:
In file included from /builds/2/corsika/corsika/framework/stack/CombinedStack.hpp:12:
In file included from /builds/2/corsika/corsika/framework/core/ParticleProperties.hpp:239:
/builds/2/corsika/corsika/detail/framework/core/ParticleProperties.inl:153:12: warning: returning address of local temporary object [-Wreturn-stack-address]
    return fmt::format("Nucleus_A{}_Z{}", A, Z);
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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