Automatically update notebooks repository on push to release

[connorjward]

Description

[francesco-ballarin]

Looks good.

Technically the change should only happen when pushing a tag, rather than on every push to release, because I only update the release install once a tag is prepared and announced. Still, there is very little point in complicating the workflow to handle that, because

1. even if the notebook repository was updated only on tag push we would still be in a chicken and egg scenario, because you first need to push the tag and once that is done I build the packages.
2. the changes in the release branch are supposed to be backward compatible (except for those on the day of a brand new release).

[connorjward]

Technically the change should only happen when pushing a tag, rather than on every push to release

Good to know. It is very easy to just move this workflow into here instead. I'll do that.