add debian/salsa-ci.yml
When essential packages introduce bugs, it hurts a large number of users of unstable. This happened here:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1021336
Uploads introducing these kind of bugs as well as the incorrect upload that attempted to fix this can be prevented, if the default salsa CI pipeline is run.
Please consider using this facility to avoid this kind of problem in the future.