Add 32-bit x86 into CI

Currently, we would need support by resolving [this issue here](https://github.com/uraimo/run-on-arch-action/issues/57) to make this happen. We definitely want to do this, as 32-bit x86 is a Tier 2 platform for GHC, and would let us avoid painful SIMD breakages and carelessness.

Edit: This is currently being worked on [here](https://github.com/uraimo/run-on-arch-action/pull/58).