How to use Hunspell in GitHub Actions

Question

I made a pull request at GitHub (isocpp/CppCoreGuidelines#1688) to replace Travis CI with GitHub Actions.
Currently, the repository has Hunspell configured using Travis CI, but it doesn't work in GitHub Actions.

It all works fine except for Hunspell. I have tried several ways to integrate it with GitHub Actions. Those are:

1. Add (in workflow file)

env:
 apt: hunspell

Didn't work.

2. Add (in workflow file)

env:
 SPELLCHECKER_PREFER_HUNSPELL: true

Didn't work either.

3. Install Hunspell separately in another command using this method.

Didn't work either.

Do you have any ideas why it isn't working?
Or how to make it work/implement it in GitHub Actions?

Thanks in advance!