CI: Update Emscripten to 3.1.10

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

(cherry picked from commit f07021fbeb7d91011c1534702042697d246551ac)

.github/workflows/javascript_builds.yml

@@ -5,7 +5,7 @@ on: [push, pull_request]
 env:
   GODOT_BASE_BRANCH: 3.x
   SCONSFLAGS: verbose=yes warnings=all werror=yes debug_symbols=no
-  EM_VERSION: 2.0.25
+  EM_VERSION: 3.1.10
   EM_CACHE_FOLDER: "emsdk-cache"
 
 concurrency: