GitHub actions needs postgresql upgrading

[wheresalice]

Overview

GitHub actions are currently failing because we are using an older version of Postgresql

Scope

Upgrade the version of postgresql being used in GitHub actions to 11.0 or later (check the Django and GitHub docs for supported versions)

Acceptance Criteria

GitHub actions no longer fail on running migrations

Questions/Assumptions

• Assumption - we can upgrade to the version being used in docker-compose (although this is currently just :latest, which we may want to set to a (more) specific version)