Include iOS artifact in `wait_for_build_release()`

[hugovk]

Include iOS artifacts here for 3.15+:

✅ Platform release managers have been notified of the commit SHA
Once the build-release workflow is complete:
- Download its artifacts from the workflow summary page.
- Copy the following files into ../cpython-3.15/3.15.0b1:
 - downloads/Python-3.15.0b1.tgz
 - downloads/Python-3.15.0b1.tar.xz
 - downloads/python-3.15.0b1-aarch64-linux-android.tar.gz
 - downloads/python-3.15.0b1-x86_64-linux-android.tar.gz
The script will continue once all files are present.

Follow on from #365.