Add github action to check that changelog has been updated

[ja573]

No description provided.

[rhigman]

Note that the third-party action used hasn't yet been updated to account for the Node v20 requirement, so we're getting warning annotations on runs e.g. https://github.com/thoth-pub/thoth/actions/runs/7889770920. Perhaps raise this as an issue with the maintainer.

[ja573]

Note that the third-party action used hasn't yet been updated to account for the Node v20 requirement, so we're getting warning annotations on runs e.g. https://github.com/thoth-pub/thoth/actions/runs/7889770920. Perhaps raise this as an issue with the maintainer.

Good point! I had assumed they didn't use node as it's just a bash script, but it's the underlying actions/checkout action that relies in node v16