Update hyperv.py

lisa/tools/hyperv.py

@@ -5,7 +5,7 @@
 import time
 from dataclasses import dataclass
 from enum import Enum
-from typing import Dict, Optional
+from typing import Dict, Optional, Set
 
 from assertpy import assert_that
 from dataclasses_json import dataclass_json
@@ -36,7 +36,7 @@ class HyperV(Tool):
     IP_REGEX = r"\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}"
     _default_switch: Optional[VMSwitch] = None
     _external_forwarding_port_start = 50000
-    _assigned_nat_ports: set[int] = set()
+    _assigned_nat_ports: Set[int] = set()
 
     @property
     def command(self) -> str:
@@ -295,7 +295,6 @@ def create_nat(self, name: str, ip_range: str) -> None:
             force_run=True,
         )
 
-
     def add_nat_mapping(self, nat_name: str, internal_ip: str) -> int:
         external_port = self._get_next_available_nat_port()