ci: override -vm-size to run the tests on GPU machines

[kzys]

Change Summary

What and Why:

GPU machines have some quirks (e.g. use Cloud Hypervisor instead of Firecracker). While most of the tests don't need GPU, running these tests would increase our coverage.

How:

Related to:

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Documentation

• [ ] Fresh Produce
• [ ] In superfly/docs, or asked for help from docs team
• [x] n/a