CI: Install a more up-to-date version of emscripten

This is to allow using more recent C++20 features in upcoming commits.
Version 3.1.6 is what is installed on Ubuntu 22.10 and works with the
C++20 features we want.

.github/workflows/wasm.yml

@@ -20,7 +20,11 @@ jobs:
       - name: "Install Ubuntu dependencies"
         run: |
           sudo apt-get update
-          sudo apt-get install -y ninja-build emscripten gcc-12 g++-12 libstdc++-12-dev
+          sudo apt-get install -y ninja-build gcc-12 g++-12 libstdc++-12-dev
+      - name: "Install emscripten"
+        uses: mymindstorm/setup-emsdk@v12
+        with:
+          version: 3.1.6
       - name: "Check versions"
         run: |
           set +e