use GitHub token by default

[eifinger]

This is done by other actions too e.g. https://github.com/peter-evans/create-pull-request/blob/5354f85616108575685a73a0ddd2f67c26a441c3/action.yml#L4-L6 and https://github.com/astral-sh/setup-uv/blob/754a7d4c2dd3b94cafffb1601b919a5705eec389/action.yml#L21-L25

[CLAassistant]

All committers have signed the CLA.