Replace changelog-linker with github_changelog_generator

[dbrumann]

https://github.com/symplify/changelog-linker is no longer maintained. I'd rather not use the suggested replacement ergebnis/github-changelog, because according to the README it will not work with squash merges, which I regularly used when a PR has more than 1 commit. The ruby gem https://github.com/github-changelog-generator/github-changelog-generator is one of the proposed alternatives.

I propose switching to github_changelog_generator and regenerate the changelog with it.

[MGatner]

I use github_changelog_generator in most of my projects. It works great when your project fits within the allowed API limits for authenticated calls, but it gets super buggy otherwise. It has caused me much heartache over at CodeIgniter4 so I recommend running it a few times (with and without token) to make sure you aren't close to the size where it will become unwieldy.