How to apt-get install in a GitHub Actions workflow?

In the new GitHub Actions, I am trying to install a package in order to use it in one of the next steps.

name: CI

on: [push, pull_request]

jobs:
  translations:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v1
      with:
        fetch-depth: 1
    - name: Install xmllint
      run: apt-get install libxml2-utils
    # ...

However this fails with

Run apt-get install libxml2-utils
  apt-get install libxml2-utils
  shell: /bin/bash -e {0}
E: Could not open lock file /var/lib/dpkg/lock-frontend - open (13: Permission denied)
E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), are you root?
##[error]Process completed with exit code 100.

What's the best way to do this? Do I need to reach for Docker?

The docs say:

The Linux and macOS virtual machines both run using passwordless sudo. When you need to execute commands or install tools that require more privileges than the current user, you can use sudo without needing to provide a password.

So simply doing the following should work:

- name: Install xmllint
  run: sudo apt-get install -y libxml2-utils