Cannot mknod: Operation not permitted

I ran into this issue trying to cache LXD containers. I had to change some file permissions because actions/cache was failing due to permission denied. Now, saving the cache works, but when I try to restore it, I get:

/usr/bin/tar -xf /opt/actions-runner/_work/_temp/f9c60f6d-08e1-489e-9f92-01f605b0ad76/cache.tzst -P -C /opt/actions-runner/_work/juju/juju --use-compress-program unzstd
/usr/bin/tar: ../../../../../var/snap/lxd/common/lxd/storage-pools/default/containers/snapcraft-juju/rootfs/dev/ptmx: Cannot mknod: Operation not permitted
...
/usr/bin/tar: Exiting with failure status due to previous errors
Warning: Failed to restore: "/usr/bin/tar" failed with error: The process '/usr/bin/tar' failed with exit code 2

Full job logs here.

Here's the relevant part of my workflow.yml:

    - run: sudo chmod -R 0777 /var/snap/lxd/common/lxd

    - name: Cache build environment
      uses: actions/cache@v4
      with:
        path: '/var/snap/lxd/common/lxd/storage-pools/default/containers/snapcraft-juju'
        key: snapcraft-build-env-${{ runner.os }}

    - run: sudo chmod -R 0777 /var/snap/lxd/common/lxd

Start with the workflow.yml excerpt and the linked job logs, focusing on the actions/cache path, the restore command, and the reported tar mknod failure. Trace how the cache action handles this path during save and restore. Done means the LXD container cache restores without the reported tar failure.