Fix to SERVER-74657 kept most threads unkillable with the following reason:
This job is primary/secondary agnostic and doesn't write to WT, stepdown won't and shouldn't interrupt it, so keep it as unkillable.

However samy.lanka@mongodb.com pointed out, the same reasoning can be made to make the thread killable preferably as this is the default.

This is used to change those threads as killable.