I believe this is a wp-cli issue.
I’m going to manually SSH into the instance and update wp-cli to the latest version. I’ll update if it helps.
It did.
I’ve root access disabled, so I used ssh [email protected] to login to the instance. Running wp cli update fails with Error: /usr/bin/wp is not writable by current user, but you can overcome that with sudo wp cli update --allow-root.
Enter your sudo password (the default is here: https://roots.io/trellis/docs/vault/), and just say yes when it asks you to.
After that the deploy worked just fine.