Installation issue: PDI along with NumPy

[tpadioleau]

Steps to reproduce the issue

Concretize the following environment.

spack:
  concretizer:
    reuse: false
    unify: true
  repos:
    builtin:
      commit: 9629cca2ad70ff3b1b63143a0c12368931e6388a
  specs:
    - 'pdi@1.10 +python'
    - 'py-numpy@2'

Error message

==> Error: failed to concretize `pdi@1.10:1+python`, `py-numpy@2` for the following reasons:

     1. Cannot satisfy 'py-numpy@2' 1(1.26.4)
     2. Cannot satisfy 'py-numpy@2' 4(1.26.4)
        required because py-numpy@2 requested explicitly 
     3. Cannot satisfy 'py-numpy@1.21.5:1' and 'py-numpy@2'
        required because pdi depends on py-numpy@1.21.5:1 when @1.10.0:+python 
          required because pdi@1.10:1+python requested explicitly 
        required because py-numpy@2 requested explicitly 
     4. Cannot satisfy 'py-numpy@1.17.4:1' and 'py-numpy@2'
        required because pdi depends on py-numpy@1.17.4:1 when +python 
          required because pdi@1.10:1+python requested explicitly 
        required because py-numpy@2 requested explicitly . You could consider setting `concretizer:unify` to `when_possible` or `false` to allow multiple versions of some packages.

Information on your system

• Spack: 1.1.1
• Builtin repo: 9629cca
• Python: 3.8.10
• Platform: linux-ubuntu20.04-icelake

Additional information

@jbigot

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