✨ Add docs and tests for Python 3.9 and Python 3.10 (#3712)

Co-authored-by: Thomas Grainger <tagrain@gmail.com>

tests/test_tutorial/test_background_tasks/test_tutorial002_py310.py

@@ -0,0 +1,21 @@
+import os
+from pathlib import Path
+
+from fastapi.testclient import TestClient
+
+from ...utils import needs_py310
+
+
+@needs_py310
+def test():
+    from docs_src.background_tasks.tutorial002_py310 import app
+
+    client = TestClient(app)
+    log = Path("log.txt")
+    if log.is_file():
+        os.remove(log)  # pragma: no cover
+    response = client.post("/send-notification/foo@example.com?q=some-query")
+    assert response.status_code == 200, response.text
+    assert response.json() == {"message": "Message sent"}
+    with open("./log.txt") as f:
+        assert "found query: some-query\nmessage to foo@example.com" in f.read()