bug#51454: Progress bar in Org source blocks

[excalamus]

> try the environment variable INSIDE_EMACS with turns off
> some fancy shell things.
>
This is a good suggestion.  Maybe I'm misunderstanding how INSIDE_EMACS works. 
The docs say:

"Emacs sets the environment variable INSIDE_EMACS in thesubshell to 
‘version,comint’, where version is theEmacs version (e.g., ‘24.1’).  Programs 
can check this variableto determine whether they are running inside an Emacs 
subshell."

https://www.gnu.org/software/emacs/manual/html_node/emacs/Interactive-Shell.html

When I check it in a session set up as described above, I get the Emacs version:

#+begin_src sh :results output :session unset
echo $INSIDE_EMACS
#+end_src

#+RESULTS:
: 
: 27.2,comint

I understand this to mean that INSIDE_EMACS *is* being set and that it's the 
guix command's responsibility to do something with it (if it wants to).

If instead I set INSIDE_EMACS to something falsey (e.g. 1) and run through 
things, I see the same result with color and control characters.