Fixed Mac M1/2 build breakage, by requiring: swig<4.

[capn-freako]

I found that the new swig (v4) was causing the same kiva build failure, as I reported in #1067.
So, I:

1. constrained swig to: "<4", in the pyproject.toml file, and
2. bumped the minor version number.

[capn-freako]

Hi @corranwebster ,

Any chance we can get this simple one merged and a rebuild posted to PyPi?
I just released a new package, which is dependent upon Enable, and this is blocking the build/installation.

Thanks!
-db
:)