Fix pg_dump sorting of foreign key constraints

Apparently, commit 04bc2c42f7 failed to notice that DO_FK_CONSTRAINT
objects require identical handling as DO_CONSTRAINT ones, which causes
some pg_upgrade tests in debug builds to fail spuriously.  Add that.

Author: Álvaro Herrera <alvherre@kurilemu.de>
Backpatch-through: 13
Discussion: https://postgr.es/m/202510181201.k6y75v2tpf5r@alvherre.pgsql

src/bin/pg_dump/pg_dump_sort.c

@@ -379,7 +379,8 @@ DOTypeNameCompare(const void *p1, const void *p2)
 		if (cmpval != 0)
 			return cmpval;
 	}
-	else if (obj1->objType == DO_CONSTRAINT)
+	else if (obj1->objType == DO_CONSTRAINT ||
+			 obj1->objType == DO_FK_CONSTRAINT)
 	{
 		ConstraintInfo *robj1 = *(ConstraintInfo *const *) p1;
 		ConstraintInfo *robj2 = *(ConstraintInfo *const *) p2;