F-Droid publication should use Github APK signature too

### Description

In https://f-droid.org/docs/Reproducible_Builds/ (section `Publishing APKs with the upstream developer’s signature`) there is a mention that we can use upstream developer signature which is nice because it would allow a user to use an APK from Github or F-droid for the same app.

### Additional context

_No response_

Read the linked F-Droid Reproducible Builds section, especially “Publishing APKs with the upstream developer’s signature,” then search this repository for the GitHub APK publication and signing workflow. Done means the published GitHub and F-Droid APKs use the same upstream developer signature and can be used interchangeably by users.

Written by the indexing model from the issue text.