Auto-update glyphsets

[yanone]

Petition to automatically update the glyphset .plist file in /sources.

I propose to find a way to automatically download the latest https://github.com/googlefonts/glyphsets/blob/main/data/results/plist/CustomFilter_GF_All.plist so that it stays up-to-date in this repo, also as part of syncing updates for downstream forks of googlefonts-project-template