Documentation/core-api: fix spelling mistake in workqueue

Correct to "following" from "followings" in the sentence "The followings
are the read bandwidths and CPU utilizations depending on different affinity
scope settings on ``kcryptd`` measured over five runs."

Signed-off-by: Attreyee Mukherjee <tintinm2017@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240110185746.24974-1-tintinm2017@gmail.com