Github changelog action is missing pull requests

[juliusknorr]

During the build of the last two pre-releases @marcoambrosini and me noticed that there were some pull requests not mentioned in the generated changelog.

E.g. #2868
is missing from https://github.com/nextcloud/nextcloud-vue/runs/7781335845?check_suite_focus=true

This seems to be partly known already, but without a clear trace on why the happens:
github-changelog-generator/github-changelog-generator#971

I've used https://github.com/lerna/lerna-changelog during the build which has less options but seems to still fit our needs and is a lot easier and faster to run locally. Not sure if we use the changelog generator anywhere else where we need more advanced features, or if we should try to replace it?

cc @nextcloud/frontenders

[skjnldsv]

Honestly, we can also decide to use whatever changelog generator.
We could also ask for the changelog file to be edited for each PR created, so we just have to release without generating anything! 🤷

This tool was to help a bit in case, but it always had some flaws

[skjnldsv]

I think it's mostly fixed now 🤔
But it should only be relevant on version bumps PRs

[susnux]

Done by github now