ci: use Ninja generator in hop of accelerating the build

.github/workflows/emscripten.yml

@@ -10,6 +10,10 @@ jobs:
       - uses: mymindstorm/setup-emsdk@v10
         with:
           version: 2.0.32
+      - name: Install ninja
+        run: |
+          sudo apt-get -y update
+          sudo apt-get install -y ninja-build
       - name: Configure CMake
         run: |
           emcmake cmake -S . -B build \
@@ -17,7 +21,8 @@ jobs:
             -DSDL_TESTS=ON \
             -DSDL_INSTALL_TESTS=ON \
             -DCMAKE_BUILD_TYPE=Release \
-            -DCMAKE_INSTALL_PREFIX=prefix
+            -DCMAKE_INSTALL_PREFIX=prefix \
+            -GNinja
       - name: Build
         run: cmake --build build/ --verbose
       - name: Run build-time tests