fix(vault): revert Vault JWT authentication not working

templates/gitlab-ci-gcloud-vault.yml

 # =====================================================================================================================
 # === Vault template variant
 # =====================================================================================================================
+variables:
+  # variables have to be explicitly declared in the YAML to be exported to the service
+  VAULT_ROLE_ID: "$VAULT_ROLE_ID"
+  VAULT_SECRET_ID: "$VAULT_SECRET_ID"
 
 .gcp-base:
   services: