Re-run pipelines leaves multiple concurrent pipelines for the same PR

[alalazo]

This was reported in Slack by @stephenmsachs

In spack/spack#37627 a few new pipelines are added. As part of CI pipelines were running here:

• https://gitlab.spack.io/spack/spack/-/pipelines/380267

Then there was a request to spackbot to "re-run pipelines", see spack/spack#37627 (comment) with subsequent reply at spack/spack#37627 (comment).

The new pipelines started here:

• https://gitlab.spack.io/spack/spack/-/pipelines/380561

concurrently with the ones above.

Expected behavior

The behavior I'd expect is that spackbot (or any other mechanism) takes care of canceling previously running pipelines before starting the new ones. This to avoid races when writing to the same buildcache.

Additional notes

The first pipeline was canceled manually on request from the user.

[alecbcs]

@scottwittenburg this sounds like a similar bug to what we all discussed at last week's meeting.