Node v26 not working in Docker image after installing Node due to missing libatomic

Describe the bug

Since Node v25 (now EOL), Node requires the libatomic1 package. See also https://github.com/npm/cli/issues/8680

If I install Node 26 with actions/setup-node, I get errors such as this:

Warning: /home/runner/_work/_tool/node/26.5.1/x64/bin/node: error while loading shared libraries: libatomic.so.1: cannot open shared object file: No such file or directory

To Reproduce

Use the latest actions-runner (Linux) image, e.g. as part of ARC scale set.

Install node:

      - name: Setup Node.js
        uses: actions/setup-node@v6
        with:
          node-version: '26'

That step/action already shows the error when expanding "Environment details"

Expected behavior

If you would preinstall libatomic1 this fix the issue. It is to be expected that people install Node.js, so it should actually work.

Runner Version and Platform

Linux AMD64 2.336.0

Start with the latest actions-runner Linux container image and its package-installation setup, then reproduce the issue using the actions/runner image and the actions/setup-node@v6 step shown here. Confirm that Node.js 26 fails before the change and runs afterward. Done means the image provides libatomic1 and the Node.js 26 environment-details step completes without the missing-library error.