Unmark port_forwarding tests as unstable

Those tests were marked as unstable after migration of CI to the
Ubuntu Focal due to related bug.
Now this bug should be fixed with depends-on patch so lets make those
tests as stable again.

Depends-On: https://review.opendev.org/756107

Change-Id: I35aebbc67d75ef609c4a8015deb8126be230bf2b
Related-Bug: #1896735
1 file changed