Add Helvetic Ruby 2026 (#1069)

Author: marcoroth

_data/conferences.yml

@@ -3159,3 +3159,13 @@
   end_date: 2026-05-30
   url: https://rubyconf.at
   announced_on: 2025-03-12
+
+- name: Helvetic Ruby 2026
+  location: Switzerland # TODO: update once location is confirmed
+  start_date: 2026-12-31 # TODO: update once dates are confirmed
+  end_date: 2026-12-31 # TODO: update once dates are confirmed
+  announced_on: 2025-05-23
+  url: https://helvetic-ruby.ch
+  twitter: helvetic_ruby
+  date_precision: year
+  mastodon: https://ruby.social/@helvetic_ruby