guix: switch from guix environment to guix shell

Summary:
See https://guix.gnu.org/manual/devel/en/html_node/Invoking-guix-environment.html.

Deprecation warning: The guix environment command is deprecated in favor of guix shell, which performs similar functions but is more convenient to use. See Invoking guix shell.

Being deprecated, guix environment is slated for eventual removal, but the Guix project is committed to keeping it until May 1st, 2023. Please get in touch with us at guix-devel@gnu.org if you would like to discuss it.

See also https://guix.gnu.org/blog/2021/from-guix-environment-to-guix-shell/
for a blog post and additional details.

Guix shell was added to guix in this commit, https://git.savannah.gnu.org/cgit/guix.git/commit/?id=80edb7df6586464aa40e84e103f0045452de95db which isn't part of the 1.3.0 release binaries out of the box, but invoking a guix pull, and updating will make it available for all builders.

This is a backport of core#26077

Backport note: since this PR there was a new guix release so the shell option is now available even without guix pull

Test Plan: HOSTS="x86_64-linux-gnu" contrib/guix/guix-build

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15503