bug#25467: Fish: some script is broken

[ng0]

Seems like a feature of our fish is currently broken, this is at
the first start, just after guix package -i fish (and no config
files present, all sitting in backups):

> fish
fish: Unknown command 'python -B 
/gnu/store/f80pivij8kfn1r49k2a3194kic3yhv7g-fish-2.4.0/share/fish/tools/create_manpage_completions.py
 --manpath --progress --cleanup-in ~/.config/fish/completions --cleanup-in 
~/.config/fish/generated_completions'
/gnu/store/f80pivij8kfn1r49k2a3194kic3yhv7g-fish-2.4.0/share/fish/functions/fish_update_completions.fish
 (line 2):      python -B $__fish_datadir/tools/create_manpage_completions.py 
--manpath --progress --cleanup-in '~/.config/fish/completions' --cleanup-in 
'~/.config/fish/generated_completions'
                                                                                
                                        ^
in function 'fish_update_completions'
        called on standard input

-- 
♥Ⓐ  ng0 -- https://www.inventati.org/patternsinthechaos/