fix: spack config get output

[cmelone]

previous output:

$ spack config get | head -12
# This is a Spack Environment file.
#
# It describes a set of packages to be installed, along with
# configuration settings.
spack:
  # add package specs to the `specs` list
  specs:
  - tcl
  - trilinos
  view: true
  concretizer:
    unify: true
==> Error: cannot dump Spack YAML configuration
[Errno 32] Broken pipe
Exception ignored in: <_io.TextIOWrapper name='<stdout>' mode='w' encoding='utf-8'>
BrokenPipeError: [Errno 32] Broken pipe

This PR cats the environment configuration directly from the spack.yaml file

[alecbcs]

Looks good to me.