Auto merge of #4087 - Turbo87:backend-labels, r=locks
Auto merge of #4087 - Turbo87:backend-labels, r=locks

renovate: Add `A-backend` to Rust PRs

... similar to what we do for JS PRs already.

rust-lang/crates.io,rust-lang/crates.io,rust-lang/crates.io,rust-lang/crates.io