bug#58798: mkdir: File exists error during substitution

[pronaip]

I think this was triggered by the laptop going to sleep and then being
woken up?

92.4 MB will be downloaded
 webkitgtk-with-libsoup2-2.36.7  22.8MiB                   44KiB/s 05:25 
[###########       ]  61.2%retrying download of 
'/gnu/store/pzkvwib98nm5vbmy132gg2m1lb0v1qbw-webkitgtk-with-libsoup2-2.36.7' 
with other substitute URLs...
 webkitgtk-with-libsoup2-2.36.7  22.8MiB                   53KiB/s 00:01 [      
            ]   0.3%guix substitute: error: mkdir: File exists
substitution of 
/gnu/store/pzkvwib98nm5vbmy132gg2m1lb0v1qbw-webkitgtk-with-libsoup2-2.36.7 
failed