ci(e2e): Run more tests on Depot (#4710)

## Description

- Sometimes I wait for my PRs to pass their tests, but my tests get
stuck queued. They aren't running, but rather waiting for a GitHub
Action Runner to open up.
- Queueing time is p50 5m and p90 18m
- I'd like to not wait for my test to run. Let's switch to depot, which
we already use and has ~3s of queueing. This gets the additional benefit
of Depot for build caching.
- This will cost us ~$400/month. However, we are moving our CI in the
near future, so this is a fleeting cost
- I ran a quick n=2 test to compare 4 vs 2 cpu, and the 4 cpu gains seem
to be ~< 10%, so using 2 cpu for now

## Release note

None.

## Migration note

None.

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Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>