gh-145177: Upgrade to Emscripten 6.0.4 (#154743)

Bumps Emscripten version for builds to 6.0.4.

Author: hoodmane

Platforms/emscripten/config.toml

@@ -1,7 +1,7 @@
 # Any data that can vary between Python versions is to be kept in this file.
 # This allows for blanket copying of the Emscripten build code between supported
 # Python versions.
-emscripten-version = "6.0.3"
+emscripten-version = "6.0.4"
 node-version = "24"
 test-args = [
     "-m", "test",