ci: 再次修复WebAssembly门禁

Author: DawningW

.github/workflows/build.yml

@@ -117,6 +117,7 @@ jobs:
       run: |
         mkdir -p install
         if [ "${{ matrix.lang }}" = "wasm" ]; then
+          embuilder build sdl2
           emcmake cmake -B build -G Ninja -DCMAKE_INSTALL_PREFIX=install -DHTTPLIB_USE_ZSTD_IF_AVAILABLE=OFF -DBUILD_DEMO=ON -DBUILD_TEST=OFF -D${{ matrix.build_option }}=ON
           cmake --build build --target CoralReefCam --parallel $(nproc)
         else