libstdc++: Add missing noexcept to lazy_split_view iterator (LWG 3593)

This was approved at the October 2021 plenary. We already have noexcept
in the other places the issue adds it in the spec.

libstdc++-v3/ChangeLog:

	* include/std/ranges (ranges::lazy_split_view::_InnerIter::end()):
	Add neoxcept (LWG 3593).

libstdc++-v3/include/std/ranges

@@ -3066,7 +3066,7 @@ namespace views::__adaptor
 	    { return _InnerIter<_Const>{_M_i}; }
 
 	    constexpr default_sentinel_t
-	    end() const
+	    end() const noexcept
 	    { return default_sentinel; }
 	  };