web-view: fix double free in has_modified_forms_cb

It's freed twice in a row in this function, oops.

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/962>


(cherry picked from commit 45d2a79c91a938295145d43d8195e245a4a5f1fc)

embed/ephy-web-view.c

@@ -3146,7 +3146,6 @@ has_modified_forms_cb (WebKitWebView *view,
   } else {
     retval = jsc_value_to_boolean (webkit_javascript_result_get_js_value (js_result));
     g_task_return_boolean (task, retval);
-    webkit_javascript_result_unref (js_result);
   }
 
 out: