Update Fairphone Checkup to be compatible with new versions of Google Android

[Korb]

Currently when viewing an Fairphone Checkup screen in F-Droid I see the following notification:

This app was built for an older version of Android and cannot be updated automatically.

I suggest you read the article "Meet Google Play's target API level requirement", which is primarily intended for Google Play users, but F-Droid users will also have difficulty finding, installing, and updating the app in situations where OS security requirements conflict with the user app.

Also, I recommend keeping in mind the changes coming in 2025.

[z3ntu]

Pushed some initial modernization to https://github.com/WeAreFairphone/FP2-Checkup/commits/dev/

targetSdk is still missing, already in targetSdk 29 some things are crashing in the Modem test page.