error in prepare-release-notes

see https://gitlab.com/sylva-projects/sylva-elements/diskimage-builder/-/jobs/10266798920:

jq: error (at <stdin>:0): Cannot index string with string "downstream_pipeline"

This happens at this place in the GitLab CI code: https://gitlab.com/sylva-projects/sylva-elements/diskimage-builder/-/blob/468c750586c4554c96b863b5db54c9928686432e/.gitlab-ci.yml#L68