ci: Replace Bun with tsx in lint-404s workflow (#17771)

Remove `oven-sh/setup-bun` and use `npx tsx` to run the lint script.
This workflow already has Node and pnpm set up, so Bun was only used
as a TypeScript runner for the final script invocation.

Part of a series of PRs to remove Bun from all CI workflows.

Co-authored-by: Claude <noreply@anthropic.com>