Update PyCon Poland CFP date

Author: kgawda

_data/conferences.yml

@@ -318,7 +318,7 @@
   year: 2025
   link: https://pl.pycon.org/2025/
   cfp_link: https://pyconpl.confreg.pl/events/40-pycon-pl-2025
-  cfp: '2025-05-15 23:59:00'
+  cfp: '2025-05-31 23:59:00'
   place: Gliwice, Poland
   start: 2025-08-28
   end: 2025-08-31