Fix the limit on the number of teams at Horsham

The Tech Day has past now, so this isn't really material, however
it's still worth correcting to avoid this error propagating if we
copy/paste this event in future.

Author: PeterJCLaw

_events/sr2025/horsham-tech-day-february.md

@@ -15,7 +15,7 @@ We provide a space for you to work in, with power and internet access, as well
 as volunteers able to help you with your kits and hands-on guidance with your
 robots.
 
-Spaces are limited to twelve teams, so be sure to [let us know][tech-day-signup]
+Spaces are limited to four teams, so be sure to [let us know][tech-day-signup]
 by Friday 7th February 2025 if you'd like to attend. We will begin confirming
 places from Wednesday 15th January 2025.