The first is that i_relallfrozen is undefined in versions earlier than 18. That's trivial to fix, we just add "0 AS relallfrozen," in the earlier versions, but still refrain from outputting it.
Ok, so long as we refrain from outputting it, I'm cool with whatever we store internally.
The second is that the pg_upgrade test (when run with olddump/oldinstall) compares the before and after dumps, and if the "before" version is 17, then it will not have the relallfrozen argument to pg_restore_relation_stats. We might need a filtering step in adjust_new_dumpfile?
That sounds trickier. Do we already have filtering steps that are sensitive to the "before" version dump?
