Add external CFP deadline for EuroSciPy 2026

Added external CFP deadline for EuroSciPy 2026.

Author: JesperDramsch

_data/conferences.yml

@@ -188,6 +188,7 @@
   link: https://euroscipy.org/
   cfp_link: https://euroscipy.org/call-for-proposals/
   cfp: '2026-02-08 23:59:00'
+  cfp_ext: '2026-03-01 23:59:00'
   tutorial_deadline: '2026-02-22 23:59:00'
   timezone: Europe/Berlin
   place: Krakow, Poland