Fix hitting docker pull limits in CI

[IvoDD]

We've had a CI run fail because it couldn't pull a docker image here.

Error looks like:

Starting mongodb service container
  /usr/bin/docker pull mongo:4.4
  Error response from daemon: toomanyrequests: You have reached your pull rate limit. You may increase the limit by authenticating and upgrading: https://www.docker.com/increase-rate-limit
  Warning: Docker pull failed with exit code 1, back off 2.721 seconds before retry.
  /usr/bin/docker pull mongo:4.4
  Error response from daemon: toomanyrequests: You have reached your pull rate limit. You may increase the limit by authenticating and upgrading: https://www.docker.com/increase-rate-limit
  Warning: Docker pull failed with exit code 1, back off 3.756 seconds before retry.
  /usr/bin/docker pull mongo:4.4
  Error response from daemon: toomanyrequests: You have reached your pull rate limit. You may increase the limit by authenticating and upgrading: https://www.docker.com/increase-rate-limit
  Error: Docker pull failed with exit code 1

If this happens again or more frequently we'll need to either decrease our docker pull calls or upgrade to a better plan.