[Helper] Fix warning in SelectableItem

[hugtalbot]

ChatGPT helped me on this one, @alxbilger I really need your 👁️ on this simple one

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[alxbilger]

@hugtalbot what was the warning?

[hugtalbot]

expression result unused about the ...

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/builds/workspace/sofa-framework/master/ubuntu_clang_default_release/src/Sofa/framework/Helper/src/sofa/helper/SelectableItem.h:250:77: warning: expression result unused [-Wunused-value]
        ((Derived::s_items[Is].key == key ? (result = Is, true) : false) || ...);
         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~    ^
/builds/workspace/sofa-framework/master/ubuntu_clang_default_release/src/Sofa/framework/Helper/src/sofa/helper/SelectableItem.h:243:16: note: in instantiation of function template specialization 'sofa::helper::SelectableItem<TestSelectableItem>::findId_impl<0UL, 1UL>' requested here
        return findId_impl(key, std::make_index_sequence<numberOfItems()>{});
               ^
/builds/workspace/sofa-framework/master/ubuntu_clang_default_release/src/Sofa/framework/Helper/src/sofa/helper/SelectableItem.h:196:25: note: in instantiation of member function 'sofa::helper::SelectableItem<TestSelectableItem>::findId' requested here
        m_selected_id = findId(key);
                        ^
/builds/workspace/sofa-framework/master/ubuntu_clang_default_release/src/Sofa/framework/Helper/test/SelectableItem_test.cpp:78:9: note: in instantiation of member function 'sofa::helper::SelectableItem<TestSelectableItem>::operator=' requested here
    foo = key_small;
        ^