Insufficient hosts for ARM64

I been looking at the Ubuntu 20.04 Stress tests (ARM64) buildvariant on the WiredTiger develop project recently as we've had a lot of tasks fail with a system failure. For example here where the task failed 10 times before stopping, and here where the task succeeds but only after 7 executions.

Talking with the team this is due to an AWS capacity issue, not with the test itself. As such, could we investigate increasing the number of ubuntu2004-arm64-large hosts?