Add rust-toolchain.toml to verified signature list

Author: kl

.github/workflows/verify-locked-down-signatures.yml

@@ -11,6 +11,7 @@ on:
       - test/Cargo.lock
       - deny.toml
       - test/deny.toml
+      - rust-toolchain.toml
       - desktop/package-lock.json
       - wireguard-go-rs/libwg/go.sum
       - ci/keys/**