GHA: Fix web gdextension build

.github/workflows/gdextension.yml

@@ -34,6 +34,8 @@ on:
 env:
   SCONS_CACHE_LIMIT: 4096
   SCONSFLAGS: dev_build=no debug_symbols=no
+  EM_VERSION: 3.1.45
+  EM_CACHE_FOLDER: "emsdk-cache"
 
 jobs:
   gdextension:
@@ -144,8 +146,27 @@ jobs:
           python-version: "3.x"
           architecture: "x64"
 
+      - name: Set up Emscripten cache
+        if: matrix.opts.platform == 'web'
+        uses: actions/cache@v3
+        with:
+          path: ${{env.EM_CACHE_FOLDER}}
+          key: ${{env.EM_VERSION}}-${{runner.os}}-libs
+
+      - name: Set up Emscripten
+        if: matrix.opts.platform == 'web'
+        uses: mymindstorm/setup-emsdk@v12
+        with:
+          version: ${{env.EM_VERSION}}
+          actions-cache-folder: ${{env.EM_CACHE_FOLDER}}
+
+      - name: Verify Emscripten setup
+        if: matrix.opts.platform == 'web'
+        run: |
+          emcc -v
+
       - name: Set up scons
-        if: matrix.opts.platform == 'windows' || matrix.opts.platform == 'macos'
+        if: matrix.opts.platform == 'windows' || matrix.opts.platform == 'macos' || matrix.opts.platform == 'web'
         run: |
           python -c "import sys; print(sys.version)"
           python -m pip install scons==4.4.0