Add spell check and update Lighthouse book (#6627)

* spellcheck config

* Merge remote-tracking branch 'origin/unstable' into spellcheck

* spellcheck update

* update spellcheck

* spell check passes

* Remove ignored and add other md files

* Remove some words in wordlist

* CI

* test spell check CI

* correct spell check

* Merge branch 'unstable' into spellcheck

* minor fix

* Merge branch 'spellcheck' of https://github.com/chong-he/lighthouse into spellcheck

* Update book

* mdlint

* delete previous_epoch_active_gwei

* Merge branch 'unstable' into spellcheck

* Tweak "container runtime" wording

* Try `BeaconState`s

.github/workflows/test-suite.yml

@@ -363,6 +363,8 @@ jobs:
       run:  CARGO_HOME=$(readlink -f $HOME) make vendor
     - name: Markdown-linter
       run: make mdlint
+    - name: Spell-check
+      uses: rojopolis/spellcheck-github-actions@v0
   check-msrv:
     name: check-msrv
     runs-on: ubuntu-latest