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

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

docs_src/encoder/tutorial001_py310.py

@@ -0,0 +1,22 @@
+from datetime import datetime
+
+from fastapi import FastAPI
+from fastapi.encoders import jsonable_encoder
+from pydantic import BaseModel
+
+fake_db = {}
+
+
+class Item(BaseModel):
+    title: str
+    timestamp: datetime
+    description: str | None = None
+
+
+app = FastAPI()
+
+
+@app.put("/items/{id}")
+def update_item(id: str, item: Item):
+    json_compatible_item_data = jsonable_encoder(item)
+    fake_db[id] = json_compatible_item_data