Fix RubyConf Austria 2026 information (#995)

* fix rubyconf austria info

* add back the website

Author: misabegovic

_data/conferences.yml

@@ -3075,19 +3075,19 @@
   mastodon: https://ruby.social/@rockymtnruby
   announced_on: 2024-10-08
 
-- name: RubyConf Austria 2025
-  location: Austria
-  # TODO: update when dates are confirmed
-  start_date: 2025-12-31
-  end_date: 2025-12-31
-  date_precision: year
-  url: https://rubyconf.at
-  announced_on: 2025-03-12
-
 - name: RubyConf TH 2026
   location: Bangkok, Thailand
   start_date: 2026-01-31
   end_date: 2026-02-01
   url: https://rubyconfth.com
   twitter: rubyconfth
   announced_on: 2025-02-28
+
+- name: RubyConf Austria 2026
+  location: Vienna, Austria
+  # TODO: update when dates are confirmed
+  start_date: 2026-05-29
+  end_date: 2026-05-31
+  date_precision: year
+  url: https://rubyconf.at
+  announced_on: 2025-03-12