`artifact.uploadArtifact` Fails with "Unable to get the ACTIONS_RUNTIME_TOKEN env variable"

Describe the Problem

Calling artifactClient.uploadArtifact results in the following error:

Error: Unable to get the ACTIONS_RUNTIME_TOKEN env variable

The Workflow File

name: FooBar

run-name: 'FooBar'

on:
  pull_request:
    branches:
      - master
    types: [opened, synchronize, reopened, ready_for_review]

jobs:
  exec-script:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout repository
        uses: actions/checkout@v4

      - name: Set up Node.js
        uses: actions/setup-node@v4
        with:
          node-version: '16'

      - name: Install dependencies
        run: npm ci

      - name: Execute the script
        run: node ./scripts/my-script.mjs
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          BASE_STATS_PATH: ./base/stats.json
          CURRENT_STATS_PATH: ./current/stats.json

Script File

import { DefaultArtifactClient } from '@actions/artifact'
import * as core from '@actions/core'
import { context, getOctokit } from '@actions/github'
import { createHTMLArtifact } from '@bundle-stats/cli-utils'
import { createJobs, createReport } from '@bundle-stats/utils'
import { readFile, writeFile } from 'fs/promises'
import process from 'node:process'

const {
	repo: { owner, repo: repoName },
	issue: { number: prNumber },
} = context
const githubToken = getEnv('GITHUB_TOKEN')
const baseStatsPath = getEnv('BASE_STATS_PATH')
const currentStatsPath = getEnv('CURRENT_STATS_PATH')
const octokit = getOctokit(githubToken)
const artifactClient = new DefaultArtifactClient()

;(async () => {
        // ...
        // Generate the report
	const bundleStatsHTML = createHTMLArtifact(jobs, report)
	await writeFile('bundle-stats.html', bundleStatsHTML)
	core.info('Uploading artifact')
	try {
		const { id: artifactId } = await artifactClient.uploadArtifact('bundle-stats-html', ['./bundle-stats.html'], './')
		if (!artifactId) {
			core.setFailed('Failed to upload artifact')
			return
		}
	} catch (error) {
		console.error(error)
	}

	// Create comment and so on...
        // ...
})()

Question

I'm unsure why calling artifactClient.uploadArtifact results in the error:

Error: Unable to get the ACTIONS_RUNTIME_TOKEN env variable

Do I need to manually set this environment variable? Or is there something missing in my workflow setup?

Start with the workflow setup and the script's artifactClient.uploadArtifact call, then inspect how @actions/artifact obtains its runtime credentials in this execution context. Reproduce the workflow and verify that the artifact uploads successfully without an unavailable environment variable; the issue provides no named repository test or source file.