Thanks to the CI team, we have just switched the trunk Android CI to build with Android API 24, which means that starting with the next trunk snapshot of the Swift SDK for Android, you will be able to build against APIs 24-27 also, if you choose (that CI run also has a link to the SDK bundle produced, which you can try using with a recent trunk build of the Swift toolchain). We already switched the trunk Windows CI which builds Android SDKs over to API 24 last month, so both trunk CI are using the same Android NDK 28c and API 24 again now. 
Thanks to @madsodgaard for getting the Foundation fixes in to make this work, and the Foundation reviewers who checked his pulls. We'll see if we can get API 23 in next, and CI work is underway for the next LTS NDK 30, currently in beta.