CP migration with gvisor extension enabled fails

[adenitiu]

What happened:
When performing the ControlPlane migration of shoots that have gvisor extension enabled, the migration is getting stuck because MR cannot be removed.

What you expected to happen:
CP migration to successfully finish.

How to reproduce it (as minimally and precisely as possible):
Create a shoot with gvisor runtime enabled and perform CP migration from one seed to another one.

Anything else we need to know?:
In order to proceed with the migration, after discussion with @plkokanov, I could
set the keepObjects field in the MR to true, then delete the MRs

Environment:

• Gardener version (if relevant):
• Extension version:
• Kubernetes version (use kubectl version):
• Cloud provider or hardware configuration:
• Others: