Switch Firefox Focus and Klar to download from Firefox CI.

The situation with Focus and Klar seems to be the same as with regular Firefox: the GitHub "latest release" does not always have APKs available (see !20 (merged)) and Firefox CI is a good alternative (FFUpdater has been using it).

Apparently my fork repository inherited the pipeline definition and automatically ran its own pipeline on this change. It looks like the download worked as intended, but I don't have things set up for the repository generation to work.

Note that even though the filenames say "unsigned", I believe the APKs are actually signed. In the case of Focus (current version 8.11.3), I confirmed that the APK contains identical files (including the signature) to the current one on the Google Play Store; for some reason, the APK itself differs. I imagine the same is true of Klar. I wasn't sure it was worth a forceFileName just to remove the "unsigned" from the name to avoid any possible confusion for users browsing the repository manually.