Draft: testing/py3-fastavro: run tests

Triggered by !54362, if we only built packages for architectures upstream were testing for we wouldn't have many packages for architectures other than x86_64.

One of the benefits of Alpine Linux for the wider community is that we do build and run tests for various architectures that upstreams don't, and also with musl, catching bugs that would otherwise go unnoticed and also providing prebuilt packages for people with various needs and wants.

But I don't want to dictate how you want to package something I myself don't use either. Here I mostly wanted to share my thoughts and am also curious as to wether tests will fail on these architectures and how. x86 was also disabled a long time ago due to failing tests.

py3-snappy or cramjam or something may still be needed for all tests to run, I haven't looked into if snappy tests could be deselected or need to be patched out until needed module happen to be packaged.