Elon Musk said he would reinstate suspended accounts on Twitter Inc.’s social-media platform, bringing back users that previously had been banned for posting hate speech, inciting violence or engaging in other behavior that violated its policies. Mr. Musk said Thursday the amnesty would begin next week, provided the accounts haven’t “broken the law or engaged in egregious spam.” He made the decision after polling users on the platform. “Vox Populi, Vox Dei,” he tweeted, a Latin phrase meaning the voice of the people is the voice of God.