chore(deps): consolidate @actions/core v3 + @actions/tool-cache v4 upgrades

[Copilot]

Combines four open Renovate PRs (#640, #657, #660, #664) into a single update, taking the latest versions of each package.

Dependency changes

• @actions/core: ^2.0.2 → ^3.0.0
• @actions/tool-cache: ^3.0.0 → ^4.0.0

Breaking change fix

@actions/core v3 restricts its exports map to the root entry point only — ./lib/summary.js is no longer accessible as a sub-path import. src/summary.ts was importing SUMMARY_ENV_VAR from that path:

// before
import {SUMMARY_ENV_VAR} from '@actions/core/lib/summary.js'

// after — inline the well-known constant directly
const SUMMARY_ENV_VAR = 'GITHUB_STEP_SUMMARY'

dist/ regenerated via npm run all.

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