libstdc++: Update __cpp_lib_adaptor_iterator_pair_constructor value

libstdc++: Update __cpp_lib_adaptor_iterator_pair_constructor value

I started implementing this feature before it was voted into the C++ WP,
and forgot to update the feature test macro after it was approved.

This defines it to the correct value, as specified in the C++23 draft.

libstdc++-v3/ChangeLog:

	* include/bits/stl_queue.h
	(__cpp_lib_adaptor_iterator_pair_constructor): Set to correct
	value.
	* include/bits/stl_stack.h
	(__cpp_lib_adaptor_iterator_pair_constructor): Likewise.
	* include/std/version
	(__cpp_lib_adaptor_iterator_pair_constructor): Likewise.
	* testsuite/23_containers/queue/cons_from_iters.cc: Update
	expected value.
	* testsuite/23_containers/stack/cons_from_iters.cc: Likewise.