Run plan without acquiring the Consul state lock

PR plan pipelines were failing with "Error acquiring the state lock"
when they collided with a concurrent apply (or another plan) holding
the lock on the same Consul-backed state.

- plan: pass -lock=false to terragrunt plan; apply keeps locking

Makefile

@@ -26,7 +26,7 @@ init:
 plan: init
 	@mkdir -p $(PLAN_DIR)
 	$(call vault_env) && \
-	terragrunt --terragrunt-working-dir $(ENV_DIR) plan -out=$(PLAN_FILE)
+	terragrunt --terragrunt-working-dir $(ENV_DIR) plan -lock=false -out=$(PLAN_FILE)
 
 apply:
 	$(call vault_env) && \