message: Use a plain array
diff: @@ -24,7 +24,7 @@ use anyhow::{anyhow, Context as _};
  use axum::{
  extract::{Extension, Path, Query},
  http::{StatusCode, Uri},
  - response::{AppendHeaders, Html, IntoResponse, Response as AxumResponse},
  + response::{Html, IntoResponse, Response as AxumResponse},
  };
  use lol_html::errors::RewritingError;
  use once_cell::sync::Lazy;
  @@ -335,7 +335,7 @@ impl RustdocPage {
  let robots = if is_latest_url { "" } else { "noindex" };
  Ok((
  StatusCode::OK,
  - AppendHeaders([("X-Robots-Tag", robots)]),
  + [("X-Robots-Tag", robots)],
  Extension(if is_latest_url {
  CachePolicy::ForeverInCdn
  } else {
  