bug#47973: Links from the cookbook to the manual are broken

[Ludovic Courtès]

Hello!

In
<https://guix.gnu.org/cookbook/fr/guix-cookbook.fr.html#Un-paquet-_00ab-hello-world-_00bb>,
“Systèmes de construction” (“Build Systems”) links to
<https://guix.gnu.org/manual/fr/guix.html#Syst_00e8mes-de-construction>,
which is 404 : it should be “guix.fr.html”, not “guix.html”.

Ludo’.