math/pdal: Fix build with gdal 3.13.0+
/wrkdirs/usr/ports/math/pdal/work/PDAL-2.8.4-src/pdal/private/gdal/Raster.cpp:698:27: error: assigning to 'char **' from 'CSLConstList' (aka 'const char *const *') discards qualifiers in nested pointer types
698 | papszMetadata = m_ds->GetMetadata(domain.c_str());
| ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~1 error generated.
Obtained from: https://github.com/PDAL/PDAL/commit/eb7220a2447c5b3d208d7ef0a76c61a17a5b21da
Approved by: portmgr (blanket)