Update to new Version 31 requirements.

src/main/java/at/bitfire/cert4android/CustomCertService.kt

@@ -244,8 +244,8 @@ class CustomCertService: Service() {
                                 .setContentText(this@CustomCertService.getString(R.string.certificate_notification_user_interaction))
                                 .setSubText(cert.subjectDN.name)
                                 .setCategory(NotificationCompat.CATEGORY_SERVICE)
-                                .setContentIntent(PendingIntent.getActivity(this@CustomCertService, id, decisionIntent, PendingIntent.FLAG_UPDATE_CURRENT))
-                                .setDeleteIntent(PendingIntent.getService(this@CustomCertService, id, rejectIntent, PendingIntent.FLAG_UPDATE_CURRENT))
+                                .setContentIntent(PendingIntent.getActivity(this@CustomCertService, id, decisionIntent, PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE))
+                                .setDeleteIntent(PendingIntent.getService(this@CustomCertService, id, rejectIntent, PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE))
                                 .build()
                         val nm = NotificationUtils.createChannels(this@CustomCertService)
                         nm.notify(CertUtils.getTag(cert), Constants.NOTIFICATION_CERT_DECISION, notify)