bug#80591: --with-branch option does not update the fine version of submodules

[Florent Pruvost]

Hi,

I realized that when using --with-branch the submodule cloned is 
checkout at the commit referenced on the main branch (master), not the 
commit referenced on the branch we want to use.
For instance:
  $ guix shell chameleon --with-branch=chameleon=release-1.1.0

the submodule "morse_cmake" is checkout at commit 
1336f7fd94a3237966251950c973bd72be0eb2f1 which is the one on master see 
https://gitlab.inria.fr/solverstack/chameleon/-/tree/master/cmake_modules?ref_type=heads, 
while on the branch 'release-1.1.0' the commit was 
37bce4cbc6b44869ec837c914b731794ad9f360c, see 
https://gitlab.inria.fr/solverstack/chameleon/-/tree/release-1.1.0/cmake_modules?ref_type=heads.

Is it something identified already ?

Thanks
Florent Pruvost