Re-enable WASM builds

[samansmink]

Should be fixed by duckdb/duckdb-rs#433 but for v1.2.0 the rust builds are failing.

This is something we should also look into preventing in the future through the duckdb-rs CI

[mlafeldt]

@samansmink Does this issue mean that building WASM extensions from Rust worked at some point?

I always thought that wasm32-unknown-unknown wasn't enough and that Emscripten would be needed. 🤔