Automatic merge from submit-queue (batch tested with PRs 57139, 57358). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

kubeadm upgrade: fix unit test flake

The CA generated for each test case is global and the cases modify
the expiry. This can flake depending on what order the tests run.

Generate a new CA for each test case.

```release-note
NONE
```

Fixes https://github.com/kubernetes/kubernetes/issues/57357

/cc @kubernetes/sig-cluster-lifecycle-bugs 
/cc @xiangpengzhao
/cc @luxas