message: Provide closed error path for unauthed preview with sites
diff: @@ -61,9 +61,8 @@ pub fn build_and_upload(
  ));
  message::warn("Falling back to unauthenticated preview.");
  if sites_preview {
  - message::warn(
  - "Note that unauthenticated preview will not preview Workers Sites.",
  - );
  + failure::bail!("Unauthenticated preview does not work for previewing Workers Sites; you need to \
  + authenticate to upload your site contents. Exiting...")
  }
  let client = http::client();
  @@ -79,7 +78,8 @@ pub fn build_and_upload(
  );
  if sites_preview {
  - message::warn("Note that unauthenticated preview will not preview Workers Sites.");
  + failure::bail!("Unauthenticated preview does not work for previewing Workers Sites; you need to \
  + authenticate to upload your site contents. Exiting...")
  }
  let client = http::client();
  