CI: Use Emscripten 3.1.59 for Web platform

Works around CI failure due to mismatch between current emsdk and older releases.

.github/workflows/web_builds.yml

@@ -7,7 +7,7 @@ env:
   # Used for the cache key. Add version suffix to force clean build.
   GODOT_BASE_BRANCH: master
   SCONSFLAGS: verbose=yes warnings=extra werror=yes debug_symbols=no
-  EM_VERSION: 3.1.39
+  EM_VERSION: 3.1.59
   EM_CACHE_FOLDER: "emsdk-cache"
 
 concurrency: