Trigger a autobuild webhook when something changes

[lazka]

In the future we might want to start some build if anything in our responses changes, maybe with some debounce to avoid triggering it too much.

• We currently already detect changes for etag handling
• We currently always "detect" a change when the appveyor job runs because it always uploads a new release and the mtime changes. We should avoid updating the parsing release if nothing has changed.

[lazka]

Since GHA only allows starting workflows with a PAT there is not much point to this. Let's wait until something changes there.