Apply go fix to simplify using modern features

This patch contains the result of running `go fix ./...`, which applies
simplifications that make use of modern language features.

There are no logic or behaviour changes.

test/util/minidns/minidns.go

@@ -1,5 +1,4 @@
 //go:build !coverage
-// +build !coverage
 
 // minidns is a trivial DNS server used for testing.
 //
@@ -63,11 +62,9 @@ func main() {
 	srv.loadZones(zonesFile)
 
 	var wg sync.WaitGroup
-	wg.Add(1)
-	go func() {
-		defer wg.Done()
+	wg.Go(func() {
 		srv.listenAndServeUDP(*addr)
-	}()
+	})
 	go func() {
 		defer wg.Done()
 		srv.listenAndServeTCP(*addr)