Steps to reproduce the issue

With a spack installation that has the recent py-cython@3.0.0:

$ spack install py-mpi4py

@adamjstewart
@pradyunsg

Error message

See spack-build-out.txt attached.

Information on your system

• Spack: 0.21.0.dev0 (d996b4d)
• Python: 3.11.2
• Platform: linux-ubuntu23.04-aarch64
• Concretizer: clingo

Additional information

spack-build-out.txt
spack-build-env.txt

General information

• I have run spack debug report and reported the version of Spack/Python/Platform
• I have run spack maintainers <name-of-the-package> and @mentioned any maintainers
• I have uploaded the build log and environment files
• I have searched the issues of this repo and believe this is not a duplicate