Update singularity.md - new date 19 feb

Author: pmitev

docs/courses_workshops/singularity.md

@@ -23,7 +23,7 @@ Please, follow the center provided [instructions](https://uppmax.github.io/Basic
 
 🌍 Place: Zoom: link will be sent to applicants
 
-📅 Date and time: 13 February, 2026: 9:15-12:00; 13:15-16:00
+📅 Date and time: 19 February, 2026: 9:15-12:00; 13:15-16:00
 
 📝 [Registration form](https://forms.gle/3XJ5xstF3rbuZyaz6)