ci: warmup ruby.wasm build with js-free version

.github/workflows/build.yml

@@ -43,6 +43,7 @@ jobs:
     - name: Build ruby.wasm
       if: steps.cache-ruby-wasm-module.outputs.cache-hit != 'true'
       run: |
+        JS=false bundle exec rbwasm build -o ruby.tmp.wasm --ruby-version 3.2
         bundle exec rbwasm build -o src/ruby.wasm --ruby-version 3.2
     - name: Build web app
       run: |