Add a wasm32 check to CI

[michaelkirk]

We did this for flatgeobuf after inadvertently breaking the wasm build: https://github.com/flatgeobuf/flatgeobuf/blob/master/.github/workflows/test.yml#L115

I think we should do it here too.

Inspired by #1476 (comment)

[urschrei]

Yep sounds like a plan.