Add Android workflow

[marcprux]

This PR adds the with_android input parameter (false by default) to run-unit-tests.yml that will use the swift-android-action to cross-compile the package for Android and run the tests in an Android emulator.

You can see a successful run of the self-test.yml workflow using this new option at: https://github.com/marcprux/ci/actions/runs/12659675167/job/35279261780

[0xTim]

I think we'll need to wait until Swift/SwiftNIO support Android before we can consider adopting Android as a (semi) supported platform in Vapor

[marcprux]

I think we'll need to wait until Swift/SwiftNIO support Android

SwiftNIO does work on Android (recently fixed in apple/swift-nio#3033). It is tested as part of @finagolfin's Android SDK builds.

before we can consider adopting Android as a (semi) supported platform in Vapor

Like with Windows and Musl, the Android build/test flag is off by default. There's certainly more work that will need to be done to add it as a supported platform, but this addition will at least permit developers to experiment with Android support in their packages easily.

[gwynne]

What developers? This workflow is used only by Vapor (for the most part).

[marcprux]

What developers? This workflow is used only by Vapor (for the most part).

My personal rationale is that I need to implement Android support for jwt-kit, which is a dependency of some other projects that are aiming to support Android (and which is currently failing). Using this workflow helped me identify an issue with apple/swift-certificates#217, which just got merged.