Update contributors.yml Galin Bistrev photo

Author: GalinBistrev2

_data/contributors.yml

@@ -25,7 +25,7 @@
 - name: Galin Bistrev
  info: "CERN Summer student 2025"
  email: [email protected]
- photo: 
+ photo: Bistrev.png
  education: "Nuclear and particle physics , Sofia University "St. Kliment  Ohridski , Bulgaria" 
  current: 1
  past_info: