New versions of F-Droid need install priority over other updates

When there’s a new version of the F-Droid app itself, this ought to download and install before any other updates are allowed to download. Otherwise, in a situation where a new F-Droid version is fixing a bug that makes it vulnerable to installing malicious software as updates to existing apps, that malicious software has an opening to be installed before the F-Droid app itself is updated to prevent that.