root zsh to bash

[mikadoZero]

I am trying to switch the root user from zsh to bash.

The relevant part of my system configuration is:

  (users (cons (user-account
          (name "guix")
          (group "users")
          (supplementary-groups '("wheel" "netdev" "audio"))
          (home-directory "/home/guix"))
               %base-user-accounts))

Reconfiguring and rebooting does not switch the shell for root.

The root user's shell is still zsh.  I know it is the zsh by it's prompt
string.

zsh is not listed as a package in the system configuration or the root
user's manifest.

`which zsh`
zsh not found

The line for root in /etc/passwd end with the shell:

/gnu/store/ia34lsanp33vaf32yhw2nnpnm2pc2g1y-zsh-5.6.2/bin/zsh

Any ideas of how I can get the root user's shell switched from zsh to
bash?