deps(ci): update actions to v4 and node to 20

[Nerixyz]

Updates actions/checkout to v4, actions/setup-node to v4 and Node.js to 20 (16 is no longer maintained).

Since this PR is pretty stale, I updated my fork to a new version of prettier (3.3.3) and all actions to the latest versions. If you want to use that fork:

- uses: Nerixyz/actionsx-prettier@v3-adj
  with:
    # prettier CLI arguments.
    args: --check .

[Nerixyz]

I'd update prettier to the latest version in a new PR after this gets merged.

[Felanbird]

@phuctm97 Do you mind taking a look at this? The ❕ on my linter actions is going to catch these hands if he doesn't stop acting so smug 😩

[Nerixyz]

@phuctm97 Can I do anything further to help you get this merged?

[davidgamero]

would love to see this merged