Submit doesn't cancel previous runs on same CL

I thought that a newer run of the same CL would cancel any old runs, but it seems it doesn't work anymore:

Perhaps caused by skipped mac os presubmit tests?

Start by reviewing the continuous-integration configuration and the handling of skipped macOS presubmit tests, using the reported screenshot as the observed behavior. Reproduce two runs for the same CL and verify that the newer run cancels the older one; done means previous runs no longer continue unexpectedly.

Written by the indexing model from the issue text.