Fix data race in MountNamespace.resolve.
Fix data race in MountNamespace.resolve.

We must hold fs.renameMu to access Dirent.parent.

PiperOrigin-RevId: 290340804

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor