CI: Update Emscripten to 3.1.10

That's the version that we'll (tentatively) use for future 3.x and 4.0
builds.

.github/workflows/javascript_builds.yml

@@ -6,7 +6,7 @@ env:
   # Only used for the cache key. Increment version to force clean build.
   GODOT_BASE_BRANCH: master
   SCONSFLAGS: verbose=yes warnings=extra werror=yes debug_symbols=no
-  EM_VERSION: 2.0.27
+  EM_VERSION: 3.1.10
   EM_CACHE_FOLDER: "emsdk-cache"
 
 concurrency: