webassembly/objpyproxy: Avoid throwing on symbol or iterator has-check.

JavaScript code uses "Symbol in object" to brand check its own proxies, and
such checks should also work on the Python side.

Signed-off-by: Andrea Giammarchi <andrea.giammarchi@gmail.com>

tests/ports/webassembly/py_proxy_has.mjs

@@ -9,3 +9,5 @@ x = []
 const x = mp.globals.get("x");
 console.log("no_exist" in x);
 console.log("sort" in x);
+console.log(Symbol.toStringTag in x);
+console.log(Symbol.iterator in x);

tests/ports/webassembly/py_proxy_has.mjs.exp

@@ -1,2 +1,4 @@
 false
 true
+false
+true