feature: add a GitHub Action

[TheGiraffe3]

Is your feature request related to a problem? Please describe.

It would be nice if this spellcheck had a GitHub Actions version. From what I'm gathering, it's easiest to run it locally; but it would be nice to have it in a workflow on GitHub as well (for example to run of pull requests).

Describe the solution you'd like

Add a GitHub Action for the spellcheck.

Describe alternatives you've considered

It would be possible to require contributors to figure out how to run the checks locally, but not ideal; this is basically "not implement it".

Additional context

N/A

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