I don't think it's a matter of trust. If Ramsdale had gotten a serious injury in the first half of the season we wouldn't have been in the conversation for second.
Arteta has been very clear that the end goal for this team is to have no "starter/backup", but that every single player should be fighting for their position every day. Raya is that player for the position of GK. I have mentioned it on another thread, but I'll say it again here.
We just have to hope this doesn't unsettle Ramsdale too much as he's still got years of potential growth to hit his peak.