Mark the STAGING option as broken - I reported this upstream and shared
a strawman patch, so hopefully this will be resolved for the next snapshot:

https://www.winehq.org/pipermail/wine-devel/2020-July/169366.html
https://www.winehq.org/pipermail/wine-devel/2020-July/169367.html

(Due to this being broken my original commit did not include the
distinfo entry for the respective download. Make up for that, in
case a fix becomes available.)

Also label the STAGING option as experimental.

PR: 247779