Tooling updates: Gradle-wrapper + Android Plugin

[juleskers]

With our new CI Gradle-plugin, Dependabot is saying that our builds are using outdated, vulnerable dependencies.

I'm fairly certain that all of those are deep in Gradle itself, so there isn't much we can do.
I wanted to see if upgrading to the latest version of plugins helps any.

The gradle-wrapper should be inspected by our fancy new wrapper-validation-action, so that's a nice test too.

In the famous words of Great Barrayaran Emperor Gregor Vorbarra, "Let's see what happens" 😄

[pserwylo]

Sounds good to me, lets see how it goes. Sometimes bumping Gradle requires changes to the F-Droid build. In fact, our recent bump through a few major versions (or perhaps it was the Android Gradle Plugin), required Java 17, which isn't on the build server. A wonderful fdroiddata maintainer fixed that for us by adding an apt-get install openjdk-17-jdk (or whatever).

I don't think this minor bump from 8.0.2 -> 8.1.0 would require anything similar, so should be an easy merge.