Update Node.js support to 18-20 from 12-16, dependencies, documentation, some practices

[danyalaytekin]

This PR if it passes review will require a major version update. I've mentioned "version 4" in a couple of places in anticipation. It:

1. makes the CI workflow pass again
2. updates Node.js support to 14-20 18-20 from 12-16
3. upgrades dependencies and native actions to latest; some of this was required for (1)
4. fixes circular dependency warnings when testing locally
5. fixes some references to older naming of this package
6. minor refactoring and fixes for documentation and code
7. quietly adds (or just acquires, with the updates) support for nektos/act; I'll add a paragraph to the readme about this in a future PR

More detail in commit log and will summarise here:

1. Dependency upgrades:
   1. Sinon upgrade was required to resolve circular dependency warnings involving fakeServer
   2. Mockery's major upgrade did not involve an API change, so should be ok
   3. Grunt doesn't require a global installation any more and I've removed that advice from the readme
   4. JSHint config has been updated a bit to latest spec, but other parts of that object may still be outdated and have no effect
2. removed unused Grunt task grunt ci; we could consider removing Grunt completely in a future PR
3. push will now trigger on both master and main in preparation for renaming the default branch
4. GitHub Actions workflow names etc were trimmed where their meaning was already represented well by their function

[danyalaytekin]

@josebolos Perhaps I could have forgone retaining Node 14 support, following @aarongoldenthal's lead in pa11y/pa11y#664, since it has passed EOL, even if it still passes in CI. Node 16 also reached EOL on September 11th 2023. What do you think?

[josebolos]

@josebolos Perhaps I could have foregone retaining Node 14 support, following @aarongoldenthal's lead in pa11y/pa11y#664, since it has passed EOL, even if it still passes in CI. Node 16 also reached EOL on September 11th 2023. What do you think?

Agreed! I think that we should only support currently supported LTS versions, so I would remove support for anything that is not Node 18 or 20 from every repo.

[danyalaytekin]

remove support for anything that is not Node 18 or 20 from every repo

@josebolos Done for this repo, noted for others! I've also removed the advice to use npm 8+ since npm 8 comes with Node 18.

84c7ec9

Removed section and added issue for discussion to pa11y/org

[josebolos]

👍