function warnOnUnknownOnlyCategories(allCategories, onlyCategories) {
  if (!onlyCategories) return;

  for (const onlyCategoryId of onlyCategories) {
    if (!allCategories?.[onlyCategoryId]) {
      log.warn('config', `unrecognized category in 'onlyCategories': ${onlyCategoryId}`);
    }
  }
}
Logs a warning if any specified onlyCategory is not a known category that can
be included.

@param {LH.Config.ResolvedConfig['categories']} allCategories
@param {string[] | null} onlyCategories
@return {void}