Fix pipeline auto-cancel preventing manual pipelines from running

This issue is a bug fix for #852 (closed). The original change would only run the pipeline on push events or anything on the main branch. This prevents manually triggered or scheduled pipelines on other branches.

This should be updated so that the pipeline always runs. The solution is to always run it except in the case of merge_request_event. Ideally this restriction should also not be there, but GitLab will not schedule the pipeline when when: always is provided as this seems to break the DAG for some reason.