Fix fetching MR CI status

The pipeline doesn't appear immediately, and so it's likely we'll hit
the assertion error. Instead, we can wait for the first pipeline fetched
to match our commit sha.

marge/job.py

@@ -123,8 +123,7 @@ def get_mr_ci_status(self, merge_request, commit_sha=None):
         )
         current_pipeline = next(iter(pipelines), None)
 
-        if current_pipeline:
-            assert current_pipeline.sha == commit_sha
+        if current_pipeline and current_pipeline.sha == commit_sha:
             ci_status = current_pipeline.status
         else:
             log.warning('No pipeline listed for %s on branch %s', commit_sha, merge_request.source_branch)