v0.2.21

Dear scverse ecosystem developers,

we overhauled the automated template sync for our cookiecutter template.
Instead of a github action in your repo that runs a cronjob, PRs are now created in a centralized fashion by @scverse-bot.
We hope the new system finally works for all (most) repos and apologize for any "noise" PRs we may have created so far. Unfortunately, the system is a bit tricky to debug -- the only real way of testing it is to trigger an actual template sync.

In case you have any questions, feel free to reach out to @grst, for instance via the scverse zulip chat.