✅ Add missing tests for code examples (#14569)

Co-authored-by: Sebastián Ramírez <tiangolo@gmail.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Nils-Hero Lindemann <nilsherolindemann@proton.me>

docs_src/dataclasses_/tutorial001_py310.py

@@ -0,0 +1,19 @@
+from dataclasses import dataclass
+
+from fastapi import FastAPI
+
+
+@dataclass
+class Item:
+    name: str
+    price: float
+    description: str | None = None
+    tax: float | None = None
+
+
+app = FastAPI()
+
+
+@app.post("/items/")
+async def create_item(item: Item):
+    return item