Update conferences.yml

https://x.com/balticruby/status/1963527516431270112

Author: marcoroth

_data/conferences.yml

@@ -3317,7 +3317,7 @@
   twitter: balticruby
   mastodon: https://ruby.social/@balticruby
   announced_on: 2025-09-02
-  cfp_open_date: 2025-09-02
+  cfp_open_date: 2025-09-04
   cfp_close_date: 2025-12-31
   cfp_link: "https://www.papercall.io/balticruby2026"