Force python3:any for arch-specific packages

* Pybuild will select python3:any for packages that are purely python
but for packages that have native code build, it selects the python
version that exists when the package is built.
* Force python3:any so that these packages aren't stuck on a specific
python3 release.

Change-Id: I0c48101b999f3a130619a4478f26517501167f5e