⚰️ Remove Python 3.8 from CI and remove Python 3.8 examples from source docs (#14559)

Co-authored-by: Yurii Motov <yurii.motov.monte@gmail.com>
Co-authored-by: Motov Yurii <109919500+YuriiMotov@users.noreply.github.com>

docs_src/schema_extra_example/tutorial005_py39.py

@@ -0,0 +1,51 @@
+from typing import Union
+
+from fastapi import Body, FastAPI
+from pydantic import BaseModel
+
+app = FastAPI()
+
+
+class Item(BaseModel):
+    name: str
+    description: Union[str, None] = None
+    price: float
+    tax: Union[float, None] = None
+
+
+@app.put("/items/{item_id}")
+async def update_item(
+    *,
+    item_id: int,
+    item: Item = Body(
+        openapi_examples={
+            "normal": {
+                "summary": "A normal example",
+                "description": "A **normal** item works correctly.",
+                "value": {
+                    "name": "Foo",
+                    "description": "A very nice Item",
+                    "price": 35.4,
+                    "tax": 3.2,
+                },
+            },
+            "converted": {
+                "summary": "An example with converted data",
+                "description": "FastAPI can convert price `strings` to actual `numbers` automatically",
+                "value": {
+                    "name": "Bar",
+                    "price": "35.4",
+                },
+            },
+            "invalid": {
+                "summary": "Invalid data is rejected with an error",
+                "value": {
+                    "name": "Baz",
+                    "price": "thirty five point four",
+                },
+            },
+        },
+    ),
+):
+    results = {"item_id": item_id, "item": item}
+    return results