https://bugs.winehq.org/show_bug.cgi?id=48354
--- Comment #5 from François Gouget fgouget@codeweavers.com --- Thatś okay. The TestBot being automated it cannot wait for the user to answer the dialog prompt to install Gecko/Mono. So it has code to prefetch the msi files in the place expected by Wine so the WinePrefix is entirely automatic.
https://source.winehq.org/git/tools.git/blob/HEAD:/testbot/lib/Build/Utils.p...
So what this bug is about is updating that code to work with shared installs.