⚰️ 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/tutorial002_py39.py

@@ -0,0 +1,19 @@
+from typing import Union
+
+from fastapi import FastAPI
+from pydantic import BaseModel, Field
+
+app = FastAPI()
+
+
+class Item(BaseModel):
+    name: str = Field(examples=["Foo"])
+    description: Union[str, None] = Field(default=None, examples=["A very nice Item"])
+    price: float = Field(examples=[35.4])
+    tax: Union[float, None] = Field(default=None, examples=[3.2])
+
+
+@app.put("/items/{item_id}")
+async def update_item(item_id: int, item: Item):
+    results = {"item_id": item_id, "item": item}
+    return results