PG::issue_repop: only adjust peer_info last_updates if not temp

Temp object repops have version eversion_t() since they don't
actually send log entries.  Updating the last_updates here
caused the peer info last_updates to be incorrect until the
next non-temp repop.

Fixes: #7718
Signed-off-by: Samuel Just <sam.just@inktank.com>