docs: Add context manager in examples of urllib.request

Author: Mr-Sunglasses

Doc/library/urllib.request.rst

@@ -1316,7 +1316,8 @@ programmatically supplied proxy URLs, and adds proxy authorization support with
 
    opener = urllib.request.build_opener(proxy_handler, proxy_auth_handler)
    # This time, rather than install the OpenerDirector, we use it directly:
-   opener.open('http://www.example.com/login.html')
+   with opener.open('http://www.example.com/login.html') as response:
+      print(response.read().decode('utf-8'))
 
 Adding HTTP headers:
 
@@ -1337,7 +1338,8 @@ every :class:`Request`.  To change this::
    import urllib.request
    opener = urllib.request.build_opener()
    opener.addheaders = [('User-agent', 'Mozilla/5.0')]
-   opener.open('http://www.example.com/')
+   with opener.open('http://www.example.com/') as response:
+      print(response.read().decode('utf-8'))
 
 Also, remember that a few standard headers (:mailheader:`Content-Length`,
 :mailheader:`Content-Type` and :mailheader:`Host`)