breaking config change

Describe the bug

252b0b46 introduced a breaking change for everyone using mkdocs.yaml instead of mkdocs.yml.

Expected behavior

Works with all possible configs provided. (check https://github.com/mkdocs/mkdocs/blob/master/mkdocs/config/base.py#L302)

Logs and/or screenshots

ci log

$ if ! grep -e '^site_url: ' mkdocs.yml; then # collapsed multi-line command
grep: mkdocs.yml: No such file or directory
$ if ! grep -e '^repo_url: ' mkdocs.yml; then # collapsed multi-line command
$ mkdocs build ${MKD_BUILD_ARGS}
ERROR   -  Config value 'site_name': Required configuration not provided.
Aborted with a configuration error!

Context & Configuration

Config-file: mkdocs.yaml

Here is the .gitlab-ci.yml file:

include:
  - component: codehub.sva.de/to-be-continuous/mkdocs/gitlab-ci-mkdocs@2.8.0
    inputs:
      requirements: "mkdocs-material"