Fix remaining Python 3.8 compatibility in assert_positions

Change list[dict[...]] to List[Dict[...]] in fixture parameter.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ctoth

tests/conftest.py

@@ -1,6 +1,6 @@
 """Shared fixtures and helpers for html_to_text tests."""
 
-from typing import Any, Dict, Union
+from typing import Any, Dict, List, Union
 
 import pytest
 
@@ -39,7 +39,7 @@ def callback(
 @pytest.fixture
 def assert_positions():
     """Helper to verify start/end positions match actual content."""
-    def _assert_positions(text: str, nodes: list[dict[str, Any]]) -> None:
+    def _assert_positions(text: str, nodes: List[Dict[str, Any]]) -> None:
         """Verify all nodes with start/end have valid positions."""
         for node in nodes:
             if "start" in node: