app-update.yml is not generated when building .zip for Linux

[adamkpickering]

This is one of the conclusions of research from #1120. app-update.yml is required for updates to work. However, it is not generated by electron-builder. This issue is for figuring out why that is, and how to fix it if possible.

[adamkpickering]

electron-userland/electron-builder#4233 is relevant to this.

[jandubois]

@adamkpickering This issue has milestone "Later" but is marked as "In-progress". Please either move it back to "Todo" if not required for the next release, or change the milestone to "Next".

[jandubois]

or change the milestone to "Next"

If this one goes to "Next", should #1624 go to "Next" as well?

[adamkpickering]

#1694 is related to this, and has been closed while I work on other things. It can be reopened once work resumes.