Commit 6ee3b5fb cleaned up most of the long/int64 confusion related to
incremental sort, but the sort debug messages were still using %ld for
int64 variables. So fix that.

Author: Haiying Tang
Backpatch-through: 13, where the incremental sort code was added
Discussion: https://postgr.es/m/4250be9d350c4992abb722a76e288aef%40G08CNEXMBPEKD05.g08.fujitsu.local