Don't skip pipelines and notes already seen
Created by: eseliger
This optimization caused problems, because we cannot ensure that resources beyond that timestamp never get updated, and in fact, they do. Hence the Pipelines would never get into their final state, because a refetch would not happen. Also, there were some state mappings missing in the GitlabPipelineState -> ChangesetCheckstate conversion.
Closes https://github.com/sourcegraph/sourcegraph/issues/12667