Use absolute path for changelog file

[wickes1]

Currently, the changelog file is in the relative path which will cause errors in the CI environment, e.g. GitHub Action. Example error:

FileNotFoundError: [Errno 2] No such file or directory: 'docs/changelog.yml'

Replace relative path with absolute path will fix it

Tested on local GitHub Action with act.

[wickes1]

GitHub Action passed with the forked version