message: chore: add as a tracing-core owner
diff: # Eliza should review everything unassigned.
  * @hawkw @tokio-rs/tracing
  +# tracing-core should include Eliza and Carl.
  +/tracing-core/ @hawkw @carllerche
  +
  # tracing-error and tracing-flame were contributed by Jane.
  /tracing-error/ @yaahc @tokio-rs/tracing
  /tracing-flame/ @yaahc @tokio-rs/tracing
  