ci-git-to-debian.yml: Fix bug on oneliner commit logs

If the commit log is oneliner, the appended "Gbp-Pq: Topic" line will be considered part of the subject. That causes the topic to be ignored during the patches export.

Fix this by ensuring a blank line is added.

Signed-off-by: Ariel D'Alessandro ariel.dalessandro@collabora.com