gh-145177: Upgrade to Emscripten 6.0.9 (#156804)

Bump Emscripten default version to 6.0.9.

Platforms/emscripten/config.toml

diff --git a/Platforms/emscripten/config.toml b/Platforms/emscripten/config.toml
index e1ffd6c..513b5ae 100644
--- a/Platforms/emscripten/config.toml
+++ b/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 = "6.0.8"
+emscripten-version = "6.0.9"
 node-version = "24"
 test-args = [
     "-m", "test",