Build/test against wasm32-wasi

GHCUp doesn't appear to have GHC 9.12. While we don't strictly speaking
need it here (it would be sufficient to test with GHC 9.10), it feels
easier to just rely on the Nix flake.

Author: SquidDev

.github/workflows/ci-wasm32-wasi.yml

@@ -0,0 +1,25 @@
+name: CI (wasm32-wasi)
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    env:
+      GHC_WASM_META: 45f73c3e075fa38efe84055b0dba87996948101d
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v31
+
+      - name: Build
+        run: |
+          nix shell gitlab:haskell-wasm/ghc-wasm-meta?host=gitlab.haskell.org&rev=${GHC_WASM_META}#{wasmtime,wasm32-wasi-cabal-9_12,wasm32-wasi-ghc-9_12} --command \
+            wasm32-wasi-cabal build
+
+      - name: Test
+        run: |
+          nix shell gitlab:haskell-wasm/ghc-wasm-meta?host=gitlab.haskell.org&rev=${GHC_WASM_META}#{wasmtime,wasm32-wasi-cabal-9_12,wasm32-wasi-ghc-9_12} --command \
+            wasm32-wasi-cabal test --project-file cabal.project.wasm32-wasi --test-wrapper ./tests/run-wasmtime.sh