Use a separate runner for light CI jobs (#5771)

.gitlab-ci/terraform.yml

@@ -22,6 +22,7 @@
 .terraform_validate:
   extends: .terraform_install
   stage: unit-tests
+  tags: [light]
   only: ['master', /^pr-.*$/]
   script:
     - terraform validate -var-file=cluster.tfvars contrib/terraform/$PROVIDER
@@ -29,6 +30,7 @@
 
 .terraform_apply:
   extends: .terraform_install
+  tags: [light]
   stage: deploy-part2
   when: manual
   only: [/^pr-.*$/]
@@ -106,6 +108,7 @@ tf-validate-aws:
 
 tf-ovh_cleanup:
   stage: unit-tests
+  tags: [light]
   image: python
   variables:
     <<: *ovh_variables