treewide: add empty default case to switch statements

We are ignoring all other possible cases, but without a proper default
case this looks like the other ones where just forgotten.

Change-Id: I7a6e490d91c4e7e8c89a2d2d2ace1a82b7c5391b
Reviewed-on: https://review.monogon.dev/c/monogon/+/2961
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
Tested-by: Jenkins CI
diff --git a/metropolis/pkg/supervisor/supervisor_processor.go b/metropolis/pkg/supervisor/supervisor_processor.go
index 816298d..b88d1a0 100644
--- a/metropolis/pkg/supervisor/supervisor_processor.go
+++ b/metropolis/pkg/supervisor/supervisor_processor.go
@@ -431,6 +431,7 @@
 			curReady = true
 		case nodeStateDead:
 			curReady = true
+		default:
 		}
 
 		if cur.state == nodeStateDead && !childrenReady {