CM-64462: use Optional instead of PEP 604 union for py3.9 compatibility

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: Ilanlido

tests/cli/commands/ai_guardrails/ides/test_copilot.py

@@ -7,6 +7,7 @@
 import json
 import os
 from pathlib import Path
+from typing import Optional
 
 from pyfakefs.fake_filesystem import FakeFilesystem
 from pytest_mock import MockerFixture
@@ -297,7 +298,7 @@ def _create_plugin_on_disk(
     fs: FakeFilesystem,
     plugin_dir: Path,
     manifest_location: str = '.github/plugin/plugin.json',
-    manifest_extra: dict | None = None,
+    manifest_extra: Optional[dict] = None,
     mcp_file: str = '.mcp.json',
     server_name: str = 'dummy-server',
 ) -> None: