Automatic merge from submit-queue (batch tested with PRs 49249, 53203, 53209, 53208, 53177). 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>.

gce:restrict file permissions for PKI assets

from 644 to 600

Fixes https://github.com/kubernetes/kubernetes/issues/52999