Add a comment about why this special case is needed.

Author: freakboy3742

Python/emscripten_trampoline.c

@@ -71,6 +71,9 @@ EM_JS(CountArgsFunc, _PyEM_GetCountArgsPtr, (), {
 // )
 
 function getPyEMCountArgsPtr() {
+    // Starting with iOS 18.3.1, WebKit on iOS has an issue with the garbage
+    // collector that breaks the call trampoline. See #130418 and
+    // https://bugs.webkit.org/show_bug.cgi?id=293113 for details.
     let isIOS = globalThis.navigator && (
         /iPad|iPhone|iPod/.test(navigator.userAgent) ||
         // Starting with iPadOS 13, iPads might send a platform string that looks like a desktop Mac.