Fix a unstable link in urllib in stdlib tutorial

[LamentXU123]

in the tutorial doc of Internet access . We've got an example of urllib.

The example script:

from urllib.request import urlopen
with urlopen('http://worldtimeapi.org/api/timezone/etc/UTC.txt') as response:
    for line in response:
        line = line.decode()             # Convert bytes to a str
        if line.startswith('datetime'):
            print(line.rstrip())         # Remove trailing newline

So if you run this example it will always return 500. I've tested it in different network environments, and the original link doesn't work at all.

cc @ZeroIntensity similar to the former fix. I've overlooked this before, sry. Skiping news and issues as well.

---

📚 Documentation preview 📚: https://cpython-previews--136296.org.readthedocs.build/

[LamentXU123]

No the link is not invalid, it's invalid in my region. Sorry for the noise >_<