ignore kw_only on Python 3.9

Author: mhils

src/h2/events.py

@@ -11,6 +11,7 @@
 from __future__ import annotations
 
 import binascii
+import sys
 from dataclasses import dataclass
 from typing import TYPE_CHECKING
 
@@ -23,6 +24,12 @@
     from .errors import ErrorCodes
 
 
+if sys.version_info < (3, 10):  # pragma: no cover
+    kw_only: dict[str, bool] = {}
+else:  # pragma: no cover
+    kw_only = {"kw_only": True}
+
+
 class Event:
     """
     Base class for h2 events.
@@ -293,7 +300,7 @@ def __repr__(self) -> str:
         )
 
 
-@dataclass(kw_only=True)
+@dataclass(**kw_only)
 class WindowUpdated(Event):
     """
     The WindowUpdated event is fired whenever a flow control window changes