`+devtools` fails to concretize on macos

[chapman39]

[exe: /Users/chapman39/dev/serac/serac_libs1/spack/bin/spack -D /Users/chapman39/dev/serac/serac_libs1/spack_env concretize --fresh ]
==> Error: concretization failed for the following reasons:

   1. Cannot select a single "version" for package "py-numpy"
[spack version: 0.22.0.dev0 (6d244b3f6776b3697861c6b5cebbee376c30bff3)
]

Only when I remove the python section from my spack.yaml, I'm able to concretize with +devtools.

Originally posted by @chapman39 in https://github.com/LLNL/serac/issues/1187#issuecomment-2259026925