Why not add devel here? In the end it doesn’t matter whether a collection uses devel (current), stable-2.19 (up to a week old), or milestone (potentially way older - personally I would not use that one, since it won’t get bugfixes for some weeks).
You can choose to test against the
stable-2.19branch, thedevelbranch, themilestonebranch, or the pre-release/released versions ofansible-core 2.19available on Pypi.