Update code examples in `docs/deployment/docker.md` to follow latest Python syntax

docs/en/docs/deployment/docker.md

@@ -145,8 +145,6 @@ There are other formats and tools to define and install package dependencies.
 * Create a `main.py` file with:
 
 ```Python
-from typing import Union
-
 from fastapi import FastAPI
 
 app = FastAPI()
@@ -158,7 +156,7 @@ def read_root():
 
 
 @app.get("/items/{item_id}")
-def read_item(item_id: int, q: Union[str, None] = None):
+def read_item(item_id: int, q: str | None = None):
     return {"item_id": item_id, "q": q}
 ```