all: fix goroutine leaks in unit tests by adding 1-elem channel buffer (#20666)

This fixes a bunch of cases where a timeout in the test would leak
a goroutine.

common/mclock/simclock_test.go

@@ -96,7 +96,7 @@ func TestSimulatedSleep(t *testing.T) {
 	var (
 		c       Simulated
 		timeout = 1 * time.Hour
-		done    = make(chan AbsTime)
+		done    = make(chan AbsTime, 1)
 	)
 	go func() {
 		c.Sleep(timeout)

eth/handler_test.go

@@ -670,7 +670,7 @@ func TestBroadcastMalformedBlock(t *testing.T) {
 	malformedEverything.TxHash[0]++
 
 	// Keep listening to broadcasts and notify if any arrives
-	notify := make(chan struct{})
+	notify := make(chan struct{}, 1)
 	go func() {
 		if _, err := sink.app.ReadMsg(); err == nil {
 			notify <- struct{}{}

p2p/server_test.go

@@ -550,7 +550,7 @@ func TestServerInboundThrottle(t *testing.T) {
 	conn.Close()
 
 	// Dial again. This time the server should close the connection immediately.
-	connClosed := make(chan struct{})
+	connClosed := make(chan struct{}, 1)
 	conn, err = net.DialTimeout("tcp", srv.ListenAddr, timeout)
 	if err != nil {
 		t.Fatalf("could not dial: %v", err)

rpc/client_test.go

@@ -297,7 +297,7 @@ func TestClientSubscribeClose(t *testing.T) {
 
 	var (
 		nc   = make(chan int)
-		errc = make(chan error)
+		errc = make(chan error, 1)
 		sub  *ClientSubscription
 		err  error
 	)