Fix Terraform version used for linting to the latest 0.13 release

CI/CD flows are failing because of backwards-incompatible changes to the linter behaviour in Terraform 0.14 compared to 0.13 (see the UGA deployment pipeline log). To avoid this, the version of Terraform used for linting should be fixed at the last 0.13 release.

Reminder: Tag head of master post-merge as v1.1.4.