Extend ignore libpng vul expiration date (#2203)

Author: caroline-ttd

.trivyignore

@@ -12,7 +12,7 @@ CVE-2025-59375 exp:2025-12-15
 CVE-2025-55163 exp:2025-10-30
 
 # UID2-6340
-CVE-2025-64720 exp:2025-12-16
+CVE-2025-64720 exp:2026-06-05
 
 # UID2-6340
-CVE-2025-65018 exp:2025-12-16
+CVE-2025-65018 exp:2026-06-05