To reproduce:

1. Change current directory to a Git checkout (e.g. `~/git/emacs' or
something).
2. From the command line:

       $ emacs --batch --eval "(progn (setf vc-git-program
\"git-is-not-installed\") (find-file-noselect \"whatever\"))"
       Error: (file-missing "Searching for program" "No such file or
directory" "git-is-not-installed")

Expected: Emacs is able to open the file, Git must not be essential.

Usecase: on the real machine Git _is_ of course installed, but then you run
Emacs inside a Docker container that has _no_ Git, with a directory mapped
from your physical machine.  In this setup there is appearance of a Git
working directory, yet Git executable is not available.

Appears to work fine up to Emacs 27, broken starting with Emacs 28.

Paul