Do not execute semrel for scheduled pipelines

Description

As of now the jobs semantic-release and semantic-release-info are also executed for scheduled pipelines. For Repositories with a bit commit history this may take some time.

Implementation ideas

We could expend the rules section of above jobs with the following rule:

    - if: $CI_PIPELINE_SOURCE == "schedule"
      when: never

I am going to propose a MR for this change.