• A developer pushes his code, opens a PR.
• His peers review it and approve the changes.
• Everybody has push access so anyone could merge it.
• Merging the PR to master would immediately deploy (if the tests pass).

Who should merge the PR and therefore approve not only the changes, but the deployment at this moment as well?

Side notes:

• We do not use feature flags (yet).
• Sometimes we need to deploy a feature only after certain event/time despite the feature being complete.
• We don't want master (for deployments), develop (to base new work) and feature branches, just a simple structure of master and feature branches.