fix build with gcc16

[nim65s]

Hi,

This follow #434 and fix:

In file included from /build/source/octomap/include/octomap/OcTreeKey.h:40,
                 from /build/source/octomap/include/octomap/OcTreeBaseImpl.h:45,
                 from /build/source/octomap/include/octomap/OccupancyOcTreeBase.h:44,
                 from /build/source/octomap/include/octomap/OcTreeStamped.h:39,
                 from /build/source/octomap/src/OcTreeStamped.cpp:34:
/nix/store/mcd6qn183lsac6dy6xqm1ijhldixvfq2-gcc-16.1.0/include/c++/16.1.0/ciso646:49:6: error: #warning "<ciso646> is not a standard header since C++20, use <version> to detect implementation-specific macros" [-Werror=cpp]
   49 | #    warning "<ciso646> is not a standard header since C++20, use <version> to detect implementation-specific macros"
      |      ^~~~~~~

The inclusion of this header does not seem to be used, as octomap now build fine for me with gcc16.