I suggest to rename our current master branch to the new GitHub standard name main.

More details on why and what has to be done here: the-turing-way/the-turing-way#1210

What do I have to do as an sktime contributor now that the renaming has happened?

Any collaborator with a local clone of the repository will need to update the clone. From the local clone of the repository on a computer, run the following commands to update the name of the default branch:

git branch -m master main
git fetch origin
git branch -u origin/main main

More info at https://docs.github.com/en/github/administering-a-repository/renaming-a-branch