Prevent DATA RACE in UnstableAttr.

The slaveInodeOperations is currently copying the object when
truncate is called (which is a no-op). This may result in a
(unconsequential) data race when being modified concurrently.

PiperOrigin-RevId: 294484276

pkg/sentry/fs/tty/slave.go

@@ -73,7 +73,7 @@ func (si *slaveInodeOperations) Release(ctx context.Context) {
 }
 
 // Truncate implements fs.InodeOperations.Truncate.
-func (slaveInodeOperations) Truncate(context.Context, *fs.Inode, int64) error {
+func (*slaveInodeOperations) Truncate(context.Context, *fs.Inode, int64) error {
 	return nil
 }