ci: Add rules:changes:compare_to to the job rules
By default MR pipelines always compare against the target branch, however branch pipelines compare the difference of the last two commit.
This means that once we merge something, jobs that we expected to run, might not depending on what the last two commits touched.
Add rules:changes:compare_to: keyword so the behavior is the same between branch and MR pipelines.
https://docs.gitlab.com/ee/ci/yaml/index.html#ruleschangescompare_to
Fixes: #3780 (closed)