Upgrade to `package:`objective_c` 4.0 #109

Job	Run time
health / breaking / run breaking health check	23s
health / changelog / run changelog health check	30s
health / license / run license health check	31s
health / coverage / run coverage health check	38s
health / do-not-submit / run do-not-submit health check	33s
health / leaking / run leaking health check	28s
health / comment	8s
	3m 11s

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