Move CI onto Node 24 actions and $GITHUB_OUTPUT

[kapantzak]

Problem

Every CI run is annotated with:

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v4, actions/checkout@v2, actions/setup-node@v2.1.2, actions/upload-artifact@v4

The reality is worse than the annotation. Two of those actions declare node12, not node20 — the runner has been silently force-upgrading them across four runtimes:

Action	Pinned	Declares	Bumped to	Declares
actions/checkout	v2	node12	v7	node24
actions/setup-node	v2.1.2	node12	v7	node24
actions/cache	v4	node20	v6	node24
actions/upload-artifact	v4	node20	v7	node24

upload-artifact needed v6 or later — v5 is still node20 and would not have cleared the warning.

Also fixed: deprecated ::set-output

Two occurrences remained in this workflow, deprecated in the same era as the Node 12 actions:

- run: echo "::set-output name=dir::$(yarn cache dir)"
- run: echo "::set-output name=BUILD_VERSION::$(jq -r .version package.json)"

Both now write to $GITHUB_OUTPUT. The step ids and output keys are unchanged, so every steps.*.outputs.* reference still resolves.

The second one matters more than it looks: BUILD_VERSION names the artifact that internal-deploy hands to Netdata Grafana Plugin Deploy in netdata/infra. If set-output is ever switched off, that breaks the deploy, not just the build.

Worth noting d3b875e ("Replace set-output with ...>>$GITHUB_OUTPUT") already did this once; it appears to have been reintroduced by the b441723 toolkit migration.

Deliberately not changed

• node-version: '20.x' — that is the Node the plugin is built with, a separate decision from the runtime the actions themselves run on. Bumping it could change build output and belongs in its own change.
• matrix.node-version in the node_modules cache key — there is no matrix in this workflow, so it interpolates to empty. Pre-existing and harmless (it just makes the key ${{ runner.os }}--nodemodules-…), left alone to keep this diff to one concern.

Verification

This PR's own CI run exercises every bumped action on the real runner — checkout, setup-node, both caches, the build, and the artifact upload. internal-deploy is gated on github.event_name == 'workflow_dispatch', so no deploy is triggered by this PR.

What CI here does not cover: the cross-repo artifact handoff. netdata/infra downloads the artifact with dawidd6/action-download-artifact@v6, and only a workflow_dispatch run reaches it. Bumping upload-artifact v4 → v7 should be transparent to that consumer, but it is the one interaction worth confirming with a manual dispatch after merge.

Suggested post-merge check:

gh workflow run ci.yml --ref master -f BRANCH=master

then confirm the run in netdata/infra downloads the artifact and completes.