The separation between the `develop` and `main` branches was inherited
from Tusky and isn't helpful, complicating the release process and
causing CI to repeatedly run the same actions on the same code.
Deprecate the `develop` branch by removing references to it in the
documentation and updating the CI configuration as necessary.
Separately, the GitHub settings will be changed to set `main` as the
default branch, and the `develop` branch will be deleted.
This action should build the APK and AAB, sign them, and store the APK
as an asset.
Uploading to the correct Google Play release track will come later.
Nik Clayton