GitHub Actions: bump Emscripten version used to build to 2.0.31.

Reference PR #6304.

.github/workflows/emscripten.yml

@@ -9,7 +9,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: mymindstorm/setup-emsdk@v10
         with:
-          version: 2.0.27
+          version: 2.0.31
       - name: Configure CMake
         run: |
           emcmake cmake -S . -B build \