std::is_trivial deprecation warnings

std::is_trivial has been deprecated in C++26. Compiling against Eigen 5.0.0 using GCC 15.2.1 and -std=gnu++26 results in a bunch of deprecation warnings such as:

/usr/include/eigen3/Eigen/src/Core/util/Serializer.h:31:52: warning: ‘template<class _Tp> struct std::is_trivial’ is deprecated: use 'is_trivially_default_constructible && is_trivially_copyable' instead [-Wdeprecated-declarations]