QFuture: fix a codechecker warning

Codechecker complains about passing a forwarding reference to std::move,
which may unexpectedly cause lvalues to be moved. We should use
std::forward instead.

This amends cbf8fc0ac4

Change-Id: Ieba9e960b5dfb448e9cebabe9541967698995b8f
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/corelib/thread/qfuture_impl.h

@@ -150,7 +150,7 @@ auto createTuple(Arg &&arg, Args &&... args)
     constexpr auto Size = sizeof...(Args); // One less than the size of all arguments
     if constexpr (QtPrivate::IsPrivateSignalArg<std::tuple_element_t<Size, TupleType>>) {
         if constexpr (Size == 1) {
-            return std::move(arg);
+            return std::forward<Arg>(arg);
         } else {
             return cutTuple(std::make_tuple(std::forward<Arg>(arg), std::forward<Args>(args)...),
                             std::make_index_sequence<Size>());