Documentation: Manual Set up test environment is outdated

[migueldivo]

Docs page: https://juju.is/docs/juju/set-up--tear-down-your-test-environment

Docs source: https://discourse.charmhub.io/t/set-up-tear-down-your-test-environment/13403

Issue: Outdated Juju Install

The manual set up includes instructions to install Juju version 3.1.2 which is currently outdated. This outdated version does not let you complete the Get started with Juju tutorial; specifically the Deploy part as the Mattermost and PostgreSQL charms are not compatible with those instructions.

Juju Version install instructions in Set up / tear down your test environment page

The Juju version installed in the Get started with Juju (Deploy section). The versions are also not consistent between both pages.