bug#53892: guix shell not reading manifest.scm when used with '--'

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hello Guix!

Consider the following:

--8<---------------cut here---------------start------------->8---
$ mkdir /tmp/test && cd /tmp/test

$ cat <<EOF > manifest.scm
(packages->manifest
 (list (specification->package "make")))
EOF

$ guix shell
guix shell: error: not loading '/tmp/test/manifest.scm' because not authorized to do so
hint: To allow automatic loading of `/tmp/test/manifest.scm' when running `guix shell', you must explicitly
authorize its directory, like so:

     echo /tmp/test >> /home/maxim/.config/guix/shell-authorized-directories

$ echo /tmp/test >> /home/maxim/.config/guix/shell-authorized-directories

$ guix shell
guix shell: loading environment from '/tmp/test/manifest.scm'...
The following derivation will be built:
   /gnu/store/886dfpr1fc43insawzbnk8s713bh9nf8-profile.drv

building CA certificate bundle...
listing Emacs sub-directories...
building fonts directory...
building directory of Info manuals...
The following builds are still in progress:
  /gnu/store/40p4vzxxmhz6ah25cx4iil3v5f87lmwn-info-dir.drv
  /gnu/store/k0jkw8rfskymq3lnkdjs9ljmccvbwcc3-fonts-dir.drv
  /gnu/store/y3y53p535v0nqvfjlzb3bw352m78xmdx-emacs-subdirs.drv

The following builds are still in progress:
  /gnu/store/40p4vzxxmhz6ah25cx4iil3v5f87lmwn-info-dir.drv
  /gnu/store/k0jkw8rfskymq3lnkdjs9ljmccvbwcc3-fonts-dir.drv

The following build is still in progress:
  /gnu/store/40p4vzxxmhz6ah25cx4iil3v5f87lmwn-info-dir.drv

building profile with 1 package...

[env]$ exit

$ guix shell -C -- make
guix shell: warning: no packages specified; creating an empty environment
guix shell: error: make: command not found
--8<---------------cut here---------------end--------------->8---

The last command exhibit the problem.

Thanks,

Maxim