Bug#976060: Migrate to udd-mirror.debian.net

[Asheesh Laroia]

Package: debian-games
Version: 3.2
X-Debbugs-CC: mattia at debian.org

Hi there!

I looked through Debian for mentions of the
public-udd-mirror.xvm.mit.edu hostname, which Mattias and I are
deprecating in favor of udd-mirror.debian.net. See also
https://lists.debian.org/debian-qa/2020/11/msg00011.html

I discovered it in debian-games via this search:
https://codesearch.debian.net/search?q=public-udd-mirror

For many years, both hostnames have worked. We now expect the old
hostname to stop working eventually.

I'm attaching a patch, which I have tested by manually running
`src/debian_games_updater.py` and validating that a list of games
appears in the file games_all.

There's some chance the patch is mangled; if so, I apologize. The
intent should be reasonably clear.

Best regards,

Asheesh.