gcc12: Fix false positives for std::vector::operator=()

[franzpoeschel]

see overload 3, the use is actually correct
https://en.cppreference.com/w/cpp/container/vector/operator=.html

First seen by @ax3l:

    inlined from 'static openPMD::Iteration::BeginStepStatus openPMD::Iteration::beginStep(std::optional<openPMD::Iteration>, openPMD::Series&, bool)' at /home/runner/work/warpx/warpx/build/_deps/fetchedopenpmd-src/src/Iteration.cpp:866:42:
/usr/include/c++/12/bits/stl_algobase.h:434:30: error: 'void* __builtin_memcpy(void*, const void*, long unsigned int)' reading between 9 and 9223372036854775807 bytes from a region of size 8 [-Werror=stringop-overread]
  434 |             __builtin_memmove(__result, __first, sizeof(_Tp) * _Num);
      |             ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/runner/work/warpx/warpx/build/_deps/fetchedopenpmd-src/src/Iteration.cpp: In static member function 'static openPMD::Iteration::BeginStepStatus openPMD::Iteration::beginStep(std::optional<openPMD::Iteration>, openPMD::Series&, bool)':
/home/runner/work/warpx/warpx/build/_deps/fetchedopenpmd-src/src/Iteration.cpp:866:42: note: at offset [0, 7] into source object '<anonymous>' of size 8
  866 |         res.iterationsInOpenedStep = {idx};
      |      

Note: I still get one false positive from pybind11, but can't do anything about that as it is not our code:

In function '__copy_m',
    inlined from '__copy_move_a2' at /nix/store/yhflz90n3xdxkzqxljmhp16rryg9w4cp-gcc-12.4.0/include/c++/12.4.0/bits/stl_algobase.h:501:30,
    inlined from '__copy_move_a1' at /nix/store/yhflz90n3xdxkzqxljmhp16rryg9w4cp-gcc-12.4.0/include/c++/12.4.0/bits/stl_algobase.h:528:42,
    inlined from '__copy_move_a' at /nix/store/yhflz90n3xdxkzqxljmhp16rryg9w4cp-gcc-12.4.0/include/c++/12.4.0/bits/stl_algobase.h:535:31,
    inlined from 'copy' at /nix/store/yhflz90n3xdxkzqxljmhp16rryg9w4cp-gcc-12.4.0/include/c++/12.4.0/bits/stl_algobase.h:626:7,
    inlined from '__uninit_copy' at /nix/store/yhflz90n3xdxkzqxljmhp16rryg9w4cp-gcc-12.4.0/include/c++/12.4.0/bits/stl_uninitialized.h:147:27,
    inlined from 'uninitialized_copy' at /nix/store/yhflz90n3xdxkzqxljmhp16rryg9w4cp-gcc-12.4.0/include/c++/12.4.0/bits/stl_uninitialized.h:185:15,
    inlined from '__uninitialized_copy_a' at /nix/store/yhflz90n3xdxkzqxljmhp16rryg9w4cp-gcc-12.4.0/include/c++/12.4.0/bits/stl_uninitialized.h:372:37,
    inlined from '_M_assign_aux' at /nix/store/yhflz90n3xdxkzqxljmhp16rryg9w4cp-gcc-12.4.0/include/c++/12.4.0/bits/vector.tcc:339:35,
    inlined from 'operator=' at /nix/store/yhflz90n3xdxkzqxljmhp16rryg9w4cp-gcc-12.4.0/include/c++/12.4.0/bits/stl_vector.h:787:21,
    inlined from 'operator()' at /home/franzpoeschel/build/gcc12/_deps/fetchedpybind11-src/include/pybind11/pybind11.h:1385:75,
    inlined from 'with_internals' at /home/franzpoeschel/build/gcc12/_deps/fetchedpybind11-src/include/pybind11/detail/internals.h:643:14,
    inlined from 'initialize' at /home/franzpoeschel/build/gcc12/_deps/fetchedpybind11-src/include/pybind11/pybind11.h:1377:23:
/nix/store/yhflz90n3xdxkzqxljmhp16rryg9w4cp-gcc-12.4.0/include/c++/12.4.0/bits/stl_algobase.h:434:30: warning: '__builtin_memcpy' reading between 9 and 9223372036854775807 bytes from a region of size 8 [-Wstringop-overread]
  434 |             __builtin_memmove(__result, __first, sizeof(_Tp) * _Num);
      |                              ^
/home/franzpoeschel/build/gcc12/_deps/fetchedpybind11-src/include/pybind11/pybind11.h: In member function 'initialize':
/home/franzpoeschel/build/gcc12/_deps/fetchedpybind11-src/include/pybind11/pybind11.h:1385:75: note: at offset [0, 7] into source object '<anonymous>' of size 8
 1385 |             internals.registered_types_py[(PyTypeObject *) m_ptr] = {tinfo};
      |                                                                           ^

[ax3l]

Works! :)
Thanks a lot!