dbase_redo: Fix Valgrind-reported memory leak

dbase_redo: Fix Valgrind-reported memory leak

Introduced by my (Álvaro's) commit 9e4f914b5eba, which was itself
backpatched to pg10, though only pg15 and up contain the problem
because of commit 9c08aea6a309.

This isn't a particularly significant leak, but given the fix is
trivial, we might as well backpatch to all branches where it applies, so
do that.

Author: Nathan Bossart <nathandbossart@gmail.com>
Reported-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/x4odfdlrwvsjawscnqsqjpofvauxslw7b4oyvxgt5owoyf4ysn@heafjusodrz7