message: use constants for header-names in axum CSP middleware
diff: @@ -172,9 +172,9 @@ pub(crate) async fn csp_middleware<B>(mut req: AxumHttpRequest<B>, next: Next<B>
  // actually enforcing them. This is useful to check if the CSP works without
  // impacting production traffic.
  if csp_report_only {
  - "Content-Security-Policy-Report-Only"
  + http::header::CONTENT_SECURITY_POLICY_REPORT_ONLY
  } else {
  - "Content-Security-Policy"
  + http::header::CONTENT_SECURITY_POLICY
  },
  rendered
  .parse()
  