Update expect to cover docs/_posts

[jsoref]

This is a 🐛 bug fix.

Summary

check-spelling is currently checking docs/ (including _posts/) but when its original corrections were landed, they ignored _posts/, so certain additional items needed to be added to expect.txt

Context

This applies #8676 (comment) (which was introduced with the landing of #8675)

[kmk3]

So I started writing #8678 before this was posted and ended afterwards; I'll
just copy part of what I said there:

Suggestion: Ignore the docs/_posts directory to avoid having to start
adding/maintaining contributor names on the dictionary.

On a related note, while I see the value in spell checking code and
documentation (which are usually the most frequently changed parts), I noticed
that in #8661 there were spelling changes done to the files in docs/_posts.
Personally, I would have refrained from doing so, as many of them are
old/historical publications (e.g.: one of the files changed is from 2013),
whose textual content I would consider rather "set in stone" at this point in
time.

[DirtyF]

@jekyll: merge +dev