[js_interop] No error on Wasm when `getProperty` returns an incompatible type

[sgrekhov]

The code below produces run-time error on dart2js but no error on dart2wasm.

main() {
  eval(r'''
    globalThis.object1 = {
      p1: 1
    };
  ''');
  print((globalContext["object1"] as JSObject).getProperty<JSString>("p1".toJS)); // On dart2js: TypeError: 1: type 'int' is not a subtype of type 'String'
}

On dart2wasm 1 is printed. I believe that there should be a run-time error on dart2wasm as well.

cc @srujzs @osa1

Dart SDK version: 3.10.0-edge.33697720bf2aba98e4ae3277e9d60d15621188b2 (main) (Sat Aug 23 14:58:03 2025 -0700) on "linux_x64"

[srujzs]

This is the same issue as #61265. getProperty has an as so this is a difference in casting behavior.