test job in tox-tests.yml file to use dind config from fragments

Currently, the test job https://gitlab.developers.cam.ac.uk/uis/devops/continuous-delivery/ci-templates/-/blob/master/auto-devops/tox-tests.yml?ref_type=heads#L62

is configured as

test:
  image: docker:git

  services:
    - docker:dind

with no env var which cause issues like this: https://gitlab.developers.cam.ac.uk/uis/devops/ssgw/webapp/-/jobs/3694803

We have ready-to-use fragment for dind and we must use it there as well.