Adapt `package:messages` to be loading mechanism independent #741

Job	Run time
health / changelog / run changelog health check	41s
health / breaking / run breaking health check	53s
health / coverage / run coverage health check	51s
health / do-not-submit / run do-not-submit health check	41s
health / license / run license health check	50s
health / leaking / run leaking health check	54s
health / comment	5s
	4m 55s

Provide feedback