fix(ci): detect breaking ci by comparing with base branch instead of main

[walldiss]

Refactor the action to:

• compare changes with target branch instead of main
• detect base branch changes to trigger ci
• don't apply kind:break! if breaking changes are detected, but there is label already
• apply kind:break! only if it is not present

TODO: tokens need permissions to write to pull requests to allow this action to set up the label