Merge pull request #40915 from akien-mga/ci-pin-emscripten

CI: Pin Emscripten version for reproducible builds

.github/workflows/javascript_builds.yml

@@ -5,7 +5,7 @@ on: [push, pull_request]
 env:
   GODOT_BASE_BRANCH: master
   SCONS_CACHE_LIMIT: 4096
-  EM_VERSION: latest
+  EM_VERSION: 1.39.20
   EM_CACHE_FOLDER: 'emsdk-cache'
 
 jobs: