Run tests on pre-existing states

Currently we create a new state for every pipeline,
however this doesn't provide coverage for states that
were already in use. Keeping a long lived state for
each branch will give us more confidence that changes
are backwards compatible.

.gitlab-ci.yml

@@ -3,7 +3,7 @@ variables:
   STABLE_IMAGE_NAME: "$CI_REGISTRY_IMAGE/stable:latest"
   BUILD_IMAGE_NAME: "$CI_REGISTRY_IMAGE/branches/$CI_COMMIT_REF_SLUG-$TERRAFORM_VERSION:$CI_COMMIT_SHA"
   RELEASE_IMAGE_NAME: "$CI_REGISTRY_IMAGE/releases/$TERRAFORM_VERSION"
-  TF_ADDRESS: "$CI_API_V4_URL/projects/$CI_PROJECT_ID/terraform/state/$CI_PIPELINE_IID-$STATE_NAME"
+  TF_ADDRESS: "$CI_API_V4_URL/projects/$CI_PROJECT_ID/terraform/state/$CI_COMMIT_REF_SLUG-$STATE_NAME"
   TFPLANTOOL_VERSION: "v0.1.0"
 
 .versions: