Automatic merge from submit-queue (batch tested with PRs 40345, 38183, 40236, 40861, 40900)

test: bump mounttest and mounttest-users images

This PR bumps two test images to latest versions:
 * mounttest to 0.8
 * mounttest-user to 0.5

It is a followup to https://github.com/kubernetes/kubernetes/pull/40613 and https://github.com/kubernetes/kubernetes/pull/40821.