Update ROSCON dates to specific start and end

Author: torydebra

www/data/conf2026.json

@@ -639,8 +639,8 @@
   {
     "shortName": "ROSCON",
     "name": "ROS Conference",
-    "start": "2026",
-    "end": "2026",
+    "start": "2026-09-22",
+    "end": "2026-09-24",
     "deadline": "",
     "city": "Toronto",
     "country": "Canada",