ci: sync GitHub Actions versions on main (checkout v4→v7, setup-node v4→v6)

[jphan32]

Summary

Follow-up to the Dependabot CI bumps that merged into dev (#1, #2). Those PRs
updated the GitHub Actions used by the workflows — but only on dev. main
still pinned the old majors in both ci.yml and release.yml:

• actions/checkout v4 → v7
• actions/setup-node v4 → v6

This keeps main's release pipeline running on the same, current action
versions Dependabot already validated on dev (CI green). After merge, main
and dev workflow files match exactly.

Why a separate PR (not waiting for the next release)

Per the git-flow model main only receives changes via PR. The bumps touch
release.yml, which runs on tags cut from main, so main should carry the
current versions independent of the next feature release.

Type of change

• Docs / chore (CI only — no plugin code or behavior change)

How was this tested?

The identical versions are already running green on dev (push + the two
Dependabot PRs). CI (validate) runs on this PR as well.

Checklist

• CI only; no main.js / styles.css / manifest.json change
• validate workflow runs on this PR
• main workflows will match dev after merge