treewide: initialize empty structs with var

Change-Id: I72d3993eaf5fe57c77b1dda8218e36a8cc11813d
Reviewed-on: https://review.monogon.dev/c/monogon/+/3108
Tested-by: Jenkins CI
Reviewed-by: Serge Bazanski <serge@monogon.tech>
diff --git a/metropolis/pkg/event/memory/example_test.go b/metropolis/pkg/event/memory/example_test.go
index 583650c..1ae12c6 100644
--- a/metropolis/pkg/event/memory/example_test.go
+++ b/metropolis/pkg/event/memory/example_test.go
@@ -82,7 +82,7 @@
 	defer ctxC()
 
 	// Create a fake NetworkService.
-	ns := NetworkService{}
+	var ns NetworkService
 
 	// Run an /etc/hosts updater. It will watch for updates from the NetworkService
 	// about the current IP address of the node.