ci: update checkout, setup-node, and cache to current majors

[katsugtgz]

Updates the CI workflow to current action versions.

Changes:

• actions/checkout v4 -> v7
• actions/setup-node v3 -> v7
• actions/cache v3 -> v6
• replaced deprecated set-output command with GITHUB_OUTPUT

Validation:

• actionlint passes on the workflow
• npm ci, npm run lint, npm run build, npm run test pass locally (110 passed, 2 skipped, pre-existing)

Scope: .github/workflows/ci.yml only.

Note: workflow runs on this PR are pending maintainer approval (first run from this fork).