ci: Ignore unused deps warning

Seen in https://buildkite.com/materialize/nightly/builds/13629#_

Author: def-

src/proto/Cargo.toml

@@ -38,4 +38,4 @@ mz-build-tools = { path = "../build-tools", default-features = false, features =
 prost-build = "0.13.5"
 
 [package.metadata.cargo-udeps.ignore]
-normal = ["workspace-hack"]
+normal = ["workspace-hack", "tokio-postgres"]