Adapt Workflow to run on PRs changing from Draft to Ready

[FlorianK13]

Right now we have this problem:

• PRs are created as draft, workflows do not trigger
• PRs are converted to "ready for review", but workflows do not trigger
• Only if there is at least one commit to the branch when the PR is already "ready for review" the Workflows trigger

Based on this source it might be possible to adapt the workflow file so that it runs on PRs that are

• ready for review
• converted from draft -> ready for review