[Systems] wiki.sugarlabs.org mediawiki code patched to fix PHP 7.4 bug

[Alex Perez]

I have applied this commit for MediaWiki manually:
https://github.com/wikimedia/mediawiki/commit/278227608808c25242c87a7092da5fb9adc50cde

After doing some quick googling, I found someone else who stated that
they'd tried applying this with an older version of mediawiki, and that
it worked for them, so I decided to try it. It's working great, and the
error log isn't filling up any more. Hopefully it stays at zero:

-rw-r----- 1 root adm 0 Jun 28 13:44
/var/log/apache2/wiki.sugarlabs.org/wiki.sugarlabs.org-error.log