fix date format (#23)

Author: aditya-shirwatkar

_data/pubs.yml

@@ -408,7 +408,7 @@
 
 - title: "Neural Control Barrier Functions from Physics Informed Neural Networks"
   authors: [Shreenabh Agrawal, Manan Tayal, Aditya Singh, Shishir Kolathaya]
-  date: 2025-4-15
+  date: 2025-04-15
   pub-type: preprint
   publisher: "Pre-print"
   pdf: https://arxiv.org/pdf/2504.11045