Method add6

tests/test_methods_and_attributes.cpp:52–52

    void add5(const ExampleMandA *other) { value += other->value; } // passing by const pointer

    void add6(int other) { value += other; }        // passing by value
    void add7(int &other) { value += other; }       // passing by reference
    void add8(const int &other) { value += other; } // passing by const reference
    // NOLINTNEXTLINE(readability-non-const-parameter) Deliberately non-const for testing