Reported on IRC, it looks like the up date of pybind11 from 2.4.3 to
2.6.1 causes openimageio to fail to build, which also prevents users
from installing/upgrading blender.

1: https://data.guix-patches.cbaines.net/compare/package-derivations?base_commit=51418c32d95d8188d8877616829f26479f1135c6&target_commit=b965b2f004d522acea17f85780e1e44c882e24b3&build_change=broken&after_name=&limit_results=40

Cc'ing Nicolas Goaziou as they might be able to provide more information
about the pybind11 update.