[CI]: TestContainerRmIptables fails binding on port

### Description

Happens regularly on the CI.

The intriguing part is that the port is obtained through `portlock`, so...

### Steps to reproduce the issue

1.
2.
3.

### Describe the results you received and expected

Not flake.

### What version of nerdctl are you using?

main

### Are you using a variant of nerdctl? (e.g., Rancher Desktop)

None

### Host information

_No response_