Switch to fine-grained personal access tokens

We use personal access tokens to have our automated documentation update the github pages repository. To improve security we should switch to the new fine-grained personal access tokens to reduce the privileges granted to the automation: https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/creating-a-personal-access-token#creating-a-fine-grained-personal-access-token