Fix #2711: Improve workflow cancellation support in CI

[BenHenning]

Fix #2711.

Per https://github.com/styfle/cancel-workflow-action#advanced-pull-requests-from-forks functionality was recently added (styfle/cancel-workflow-action#55) to:

1. Allow cancellation based on workflows starting (regardless of where they start)
2. Remove the need for the access token, allowing proper fork support (I actually thought this wasn't an issue, but maybe we didn't realize it before)

Both should substantially reduce actions time since subsequent commits should properly cancel everything previous run, both for forks & non-forks. I'm expecting this to fix #2711 but I will need to verify in this PR.

[BenHenning]

Hmm it seems like the canceller is not running (all cancelled workflows in the last 2 commits were manual). Will need to dig into why.

PR is probably going to be put on hold for a few days (until I get a brief moment to be able to get back to it).

[oppiabot]

Hi @BenHenning, I'm going to mark this PR as stale because it hasn't had any updates for 7 days. If no further activity occurs within 3 days, it will be automatically closed so that others can take up the issue.
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