Add heise devSec (tech-conferences#8290)

Author: prigara

conferences/2026/security.json

@@ -195,6 +195,18 @@
     "online": false,
     "locales": "EN"
   },
+  {
+    "name": "heise devSec",
+    "url": "https://heise-devsec.de/cfp.php",
+    "startDate": "2026-09-22",
+    "endDate": "2026-09-23",
+    "city": "Marburg",
+    "country": "Germany",
+    "online": false,
+    "locales": "DE",
+    "cfpUrl": "https://heise-devsec.de/code_of_conduct.php",
+    "cfpEndDate": "2026-04-14"
+  },
   {
     "name": "AMTSO Cyber Research Conference",
     "url": "https://www.amtso.org/special-events/amtso-cyber-research-conference-2026",