📝 Update source examples and docs from Python 3.9 to 3.10 (#14900)

docs_src/async_tests/app_a_py310/main.py

@@ -0,0 +1,8 @@
+from fastapi import FastAPI
+
+app = FastAPI()
+
+
+@app.get("/")
+async def root():
+    return {"message": "Tomato"}

docs_src/async_tests/app_a_py310/test_main.py

@@ -0,0 +1,14 @@
+import pytest
+from httpx import ASGITransport, AsyncClient
+
+from .main import app
+
+
+@pytest.mark.anyio
+async def test_root():
+    async with AsyncClient(
+        transport=ASGITransport(app=app), base_url="http://test"
+    ) as ac:
+        response = await ac.get("/")
+    assert response.status_code == 200
+    assert response.json() == {"message": "Tomato"}