ci: bump actions/checkout, setup-go, setup-node to latest majors

[abienkowski]

Problem

release-verify (and CI generally) logs deprecation warnings:

Node.js 20 is deprecated. The following actions target Node.js 20 but are
being forced to run on Node.js 24: actions/checkout@v4, actions/setup-go@v5,
actions/setup-node@v4.

GitHub is deprecating Node 20 on Actions runners (see changelog).

Fix

Bumped all three actions to their latest major versions, all of which declare using: node24:

• actions/checkout v4 → v7
• actions/setup-go v5 → v7
• actions/setup-node v4 → v7

Checked each intermediate major's release notes for breaking changes relevant to this repo:

• setup-go v6 changed toolchain-selection handling — doesn't affect us since we pass a fixed go-version (1.22) matching go.mod's go 1.22 line, with no toolchain directive.
• setup-node v5/v6 changed npm caching behavior — doesn't affect us since we already pass cache: npm explicitly and ts/package.json has no packageManager field.
• checkout v5/v6/v7 — no behavioral changes relevant to this repo (persisted-credentials-file change, ESM migration, etc.).

Verification

All 6 CI checks + the workflow-syntax itself will confirm this in the PR run.