Build failure: qgis-ltr build is failing after libxml2 upgrade

[imincik]

Steps To Reproduce

Steps to reproduce the behavior:

1. build qgis-ltr with latest master branch

nix-build -A qgis-ltr

Build log

/build/source/pdal/XMLSchema.cpp: In member function 'bool pdal::XMLSchema::validate(xmlDocPtr, const std::string&)':
/build/source/pdal/XMLSchema.cpp:257:9: error: invalid conversion from 'void (*)(void*, xmlErrorPtr)' {aka 'void (*)(void*, _xmlError*)'} to 'xmlStructuredErrorFunc' {aka 'void (*)(void*, const _xmlError*)'} [-fpermissive]
  257 |         &SchemaParserStructuredErrorHandler, m_global_context);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |         |
      |         void (*)(void*, xmlErrorPtr) {aka void (*)(void*, _xmlError*)}
In file included from /build/source/pdal/XMLSchema.hpp:50,
                 from /build/source/pdal/XMLSchema.cpp:34:
/nix/store/iqjsxkcdnvvz1bfpq960ygicc5clz9hv-libxml2-2.12.3-unstable-2023-12-14-dev/include/libxml2/libxml/xmlschemas.h:156:65: note:   initializing argument 2 of 'void xmlSchemaSetParserStructuredErrors(xmlSchemaParserCtxtPtr, xmlStructuredErrorFunc, void*)'
  156 |                                          xmlStructuredErrorFunc serror,
      |                                          ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~
[ 39%] Building CXX object CMakeFiles/pdal_base.dir/filters/private/csf/Constraint.cpp.o
[ 39%] Building CXX object CMakeFiles/pdal_base.dir/filters/private/csf/Particle.cpp.o
[ 39%] Building CXX object CMakeFiles/pdal_base.dir/filters/private/csf/Rasterization.cpp.o
[ 39%] Building CXX object CMakeFiles/pdal_base.dir/filters/private/csf/XYZReader.cpp.o
[ 39%] Building CXX object CMakeFiles/pdal_base.dir/filters/private/csf/c2cdist.cpp.o
[ 40%] Building CXX object CMakeFiles/pdal_base.dir/filters/private/csf/point_cloud.cpp.o
[ 40%] Building CXX object CMakeFiles/pdal_base.dir/filters/private/delaunator.cpp.o
[ 40%] Building CXX object CMakeFiles/pdal_base.dir/filters/private/expr/AssignParser.cpp.o
[ 40%] Building CXX object CMakeFiles/pdal_base.dir/filters/private/expr/AssignStatement.cpp.o
[ 40%] Building CXX object CMakeFiles/pdal_base.dir/filters/private/expr/BaseParser.cpp.o
[ 40%] Building CXX object CMakeFiles/pdal_base.dir/filters/private/expr/ConditionalExpression.cpp.o
make[2]: *** [CMakeFiles/pdal_base.dir/build.make:2386: CMakeFiles/pdal_base.dir/pdal/XMLSchema.cpp.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [CMakeFiles/Makefile2:739: CMakeFiles/pdal_base.dir/all] Error 2
make: *** [Makefile:166: all] Error 2

Additional context

qgis-ltr is building with the older version of pdal (2.5), because it can't build with the latest version (see: qgis/QGIS#54940). Build of pdal 2.5 started to fail after recent libxml2 update to version 2.12.

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[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/week-in-geospatial-team/37035/3