CI is slow due to blis release

[anakin87]

Problem

Our unit tests in the CI got significantly slower. Two examples ⬇

Today:
Tests / Unit / ubuntu-latest - 10m
Tests / Unit / windows-latest - 16m
Tests / Unit / macos-latest - 3m

Yesterday:
Tests / Unit / ubuntu-latest - 3m
Tests / Unit / windows-latest - 5m
Tests / Unit / macos-latest - 3m

Investigation

I investigated the dependency resolution locally, running hatch env prune and hatch -vv -e test shell to recreate the test environment with python 3.9.

I noticed that much time was spent building blis from source.

Thanks to pipedtree, I discovered that blis is a dependency of thinc, required by spacy.

bls==1.2.1 was released today, but they don't provide pre-built wheels for python 3.9.

For this reason, the library is compiled from source and this process requires much time.

Pinning blis<1.2.1 for python 3.9 is a potential solution.