🐞 bug: in rare cases, we might deploy an older commit than intended

[larwaa]

Describe the bug

We have restrictions on concurrency for our deploy job, but if an older PR finishes the rest of the pipeline after a later PR, then that PR will be deployed even though it should've been cancelled.

To Reproduce

Steps to reproduce the behavior:

1. Merge a PR that finishes it's tests slowly
2. Merge a PR that finishes it's tests quickly
3. Cross your fingers that the timing matches up for this issue to occur
4. See that the older commit is deployed after the latest commit

Expected behavior

A later commit should always be deployed after an older commit