Add spell checking GitHub Actions workflow

[ydah]

This PR adds spell checking GitHub Actions workflow and fixes typos.

How about the following spell check by CI?

• https://github.com/codespell-project/codespell

The run detected the following spelling errors:

https://github.com/ruby/lrama/actions/runs/6520864200/job/17708868735?pr=120

Error: ./lib/lrama/context.rb:173: lenght ==> length
Error: ./lib/lrama/context.rb:217: assinged ==> assigned
Error: ./lib/lrama/context.rb:262: replase ==> replace, relapse, rephase
Error: ./lib/lrama/context.rb:275: replase ==> replace, relapse, rephase

[yui-knk]

Seem good, let's try it.