doc: Add CONFIG_RCU_STRICT_GRACE_PERIOD to checklist.rst

This commit adds CONFIG_RCU_STRICT_GRACE_PERIOD to the list of debugging
Kconfig options in checklist.rst.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>