Add --no-sync to pg_upgrade's uses of pg_dump and pg_dumpall.

Add --no-sync to pg_upgrade's uses of pg_dump and pg_dumpall.

There's no reason to ensure that the files pg_upgrade generates
with pg_dump and pg_dumpall have been written safely to disk.  If
there is a crash during pg_upgrade, the upgrade must be restarted
from the beginning; dump files left behind by previous pg_upgrade
attempts cannot be reused.

Reviewed-by: Peter Eisentraut, Tom Lane, Michael Paquier, Daniel Gustafsson
Discussion: https://postgr.es/m/20240503171348.GA1731524%40nathanxps13