🔧 Minor type annotation fix (#259)

Author: chrisjsewell

markdown_it/_compat.py

@@ -4,7 +4,8 @@
 import sys
 from typing import Any
 
+DATACLASS_KWARGS: Mapping[str, Any]
 if sys.version_info >= (3, 10):
-    DATACLASS_KWARGS: Mapping[str, Any] = {"slots": True}
+    DATACLASS_KWARGS = {"slots": True}
 else:
-    DATACLASS_KWARGS: Mapping[str, Any] = {}
+    DATACLASS_KWARGS = {}