fix failed test by `reserve space` (#7030)
fix failed test by `reserve space` (#7030)

Signed-off-by: Little-Wallace <497982b90fc38d39ce68f17ad0ca96c20b76c81b@gmail.com>
c4pt0r/tikv,pingcap/tikv,BusyJay/tikv,pingcap/tikv,BusyJay/tikv,BusyJay/tikv,BusyJay/tikv