Flakiness around E2E private registry test

[dereknola]

Is your feature request related to a problem? Please describe.

The E2E Private Registry Test suffers from flaky failures around the cleanup of the docker registry container. Several examples of failure:
https://github.com/k3s-io/k3s/actions/runs/10269825266
https://github.com/k3s-io/k3s/actions/runs/10222376239
https://github.com/k3s-io/k3s/actions/runs/10373502859

The test typical passes after 1-2 restarts, but that slows down PR acceptance.

Describe the solution you'd like
Reduce or eliminate the failures seen on test cleanup.

Describe alternatives you've considered

Additional context