reproducible Debian: mark cbxi4a-armhf as down

Signed-off-by: Holger Levsen <holger@layer-acht.org>

jenkins-home/offline_nodes

@@ -14,6 +14,8 @@
 # Also see https://pad.sfconservancy.org/p/rb-build-nodes-keep
 
 # investigation needed
+## tried power-cycling several times:
+# cbxi4a-armhf-rb.debian.net
 
 # Down here nodes are automatically added by the maintenance job when they have
 # been failing their health check or maintenance job for too long.