Migrate workflows to use `peter-evans/create-pull-request@v7`

[vitorvasc]

Currently, some of our workflows rely on different approaches to create pull requests. The auto-update-community-members.yml relies on peter-evans/create-pull-request.

This action is actively maintained by a GitHub employee, regularly updated, and provides a reliable way to create/update pull requests within CI pipelines.

We've already discussed it in the docs-approvers Slack channel: https://cloud-native.slack.com/archives/C06EDFPQ5EH/p1758019249477619?thread_ts=1758017672.876119&cid=C06EDFPQ5EH

/cc @open-telemetry/docs-maintainers

[theletterf]

Trying to assign this to our trusty Copilot. :)