tests: Skip test_snapshot_restore_with_fd on aarch64

`test_snapshot_restore_with_fd` uses unsafe file descriptors and with
rust 1.82.0 it errors with:

```
fatal runtime error: IO Safety violation: owned file descriptor already
closed
```

so has been skipped for now.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>

tests/integration.rs

@@ -7587,6 +7587,7 @@ mod common_sequential {
     }
 
     #[test]
+    #[cfg_attr(target_arch = "aarch64", ignore = "See #6970")]
     fn test_snapshot_restore_with_fd() {
         let focal = UbuntuDiskConfig::new(FOCAL_IMAGE_NAME.to_string());
         let guest = Guest::new(Box::new(focal));