Disable the Welcome to Gradle message

Changes

The message below prints when Gradle runs for the first time...which is every time in CI; squash this message since it is relevant.
```
Welcome to Gradle 8.2!
```

Here are the highlights of this release:

Kotlin DSL: new reference documentation, assignment syntax by default
Kotlin DSL is now the default with Gradle init
Improved suggestions to resolve errors in console output

For more details see https://docs.gradle.org/8.2/release-notes.html

Starting a Gradle Daemon, 1 stopped Daemon could not be reused, use --status for details


This message showing in CI recently: https://github.com/beeware/.github/actions/runs/8013325227/job/21891321580?pr=99#step:28:392
This message not showing in CI any longer with this PR: https://github.com/beeware/briefcase-android-gradle-template/actions/runs/8013748771/job/21891259687?pr=85#step:25:391

## PR Checklist:
<!--- Go over all the following points, and put an `x` in all the boxes that apply. -->
- [X] All new features have been tested
- [X] All new features have been documented
- [X] I have read the **CONTRIBUTING.md** file
- [X] I will abide by the code of conduct

beeware / briefcase-android-gradle-template

Disable the Welcome to Gradle message #85

Changes