This is a punt at fixing https://github.com/vector-im/element-web/issues/12433,
on the assumption that multiple update checks might collide with a
download which are already queued to install. It also avoids repeatedly
re-downloading the same update on every check, as per the Note: on
https://github.com/electron/electron/blob/main/docs/api/auto-updater.md#autoupdatercheckforupdates
However, it means that you may have to upgrade twice if you wait more than 24h to install
a new build - and if you cancel an upgrade prompt, you'll have to either restart
the app or explicitly check for a new version to get upgrades working again.
However, this is less annoying than having the app fail to relaunch after upgrading.
