Bump github_changelog_generator
Bump github_changelog_generator

Bumps [github_changelog_generator](https://github.com/github-changelog-generator/Github-Changelog-Generator) from 20ee04ba1234e9e83eb2ffb5056e23d641c7a018 to 1.15.2. This release includes the previously tagged commit.
- [Release notes](https://github.com/github-changelog-generator/Github-Changelog-Generator/releases)
- [Changelog](https://github.com/github-changelog-generator/github-changelog-generator/blob/master/CHANGELOG.md)
- [Commits](https://github.com/github-changelog-generator/Github-Changelog-Generator/commits/v1.15.2)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
puppetlabs/puppetlabs-motd