fix: PAAL-206 Configure anyio to only use asyncio backend

Author: qa-jil-kamerling

adk/tests/test_a2a_starlette.py

@@ -1,3 +1,4 @@
+from typing import Any
 from unittest.mock import AsyncMock, Mock
 
 import pytest
@@ -43,13 +44,13 @@ def test_agent_card_endpoint(self, starlette_app: Starlette, client: TestClient)
 
 class TestTelemetryFilter:
     """Test suite for the TelemetryFilter class."""
-    async def create_telemetry_filter(self, app_mock):
+    async def create_telemetry_filter(self, app_mock: AsyncMock) -> TelemetryFilter:
         return TelemetryFilter(
             app=app_mock,
             filtered_paths={"/.well-known/agent-card.json"}
         )
 
-    async def simulate_request(self, path):
+    async def simulate_request(self, path: str) -> tuple[Mock, dict[str, Any], Mock]:
         scope = {"type": "http", "path": path}
         receive = Mock()
         send = Mock()