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
7e22151db7