fix(config): fix package-json configuration

[romanhrynevych]

Noticed that if I want to config this package inside my root package.json nothing worked, so look through official unjs/c12 docs and noticed that if we want to import from package.json need to set option to true, link to anchor:

Don't know how to test it, but think this will fixed it ❤️

const config = await loadConfig<ChangelogOptions>({
    name: 'changelogithub',
    defaults: defaultConfig,
    overrides: options,
    // added this 👇  
    packageJson: true,
  }).then(r => r.config || defaultConfig)