[nit]: update ginkgo version in CI process keep same with go mod

[SamYuan1990]

try to fix warning as https://github.com/sustainable-computing-io/kepler/actions/runs/11903667506/job/33171074065#step:7:451

and a nil pointer in test code.

[github-actions]

🤖 SeineSailor

Here is a concise summary of the pull request changes:

This pull request updates the Ginkgo version in the CI process to v2.20.1, resolving a warning and a nil pointer issue in the test code. The changes include updating the ginkgo-set target in the Makefile and introducing a BeforeEach function call in the vm_stats_test.go file to ensure proper configuration initialization and prevent nil pointer errors. Overall, these changes improve the reliability and stability of the test suite.