Update checkout and setup-node to current majors in CI workflow

[katsugtgz]

Updates actions/checkout to v7 and actions/setup-node to v7 in the CI workflow.

Evidence:

• .github/workflows/ci.yml referenced actions/checkout@v3 and actions/setup-node@v2
• current stable releases are checkout v7.0.1 and setup-node v7.0.0

Validation:

• workflow YAML parses after the change
• the node 18 step and the deno step are unchanged

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

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[katsugtgz]

Sorry for the churn. setup-deno v2 is out, so I pushed the remaining bump to v2.0.5. The pinned deno-version 1.40.2 is unaffected.