fn: GoroutineManager.Go returns bool, not error

This was requested in https://github.com/lightningnetwork/lnd/pull/9140#discussion_r1821181787

fn/goroutine_manager_test.go

@@ -20,7 +20,7 @@ func TestGoroutineManager(t *testing.T) {
 
 	taskChan := make(chan struct{})
 
-	require.NoError(t, m.Go(func(ctx context.Context) {
+	require.True(t, m.Go(func(ctx context.Context) {
 		<-taskChan
 	}))
 
@@ -38,7 +38,7 @@ func TestGoroutineManager(t *testing.T) {
 	require.Greater(t, stopDelay, time.Second)
 
 	// Make sure new goroutines do not start after Stop.
-	require.ErrorIs(t, m.Go(func(ctx context.Context) {}), ErrStopping)
+	require.False(t, m.Go(func(ctx context.Context) {}))
 
 	// When Stop() is called, the internal context expires and m.Done() is
 	// closed. Test this.
@@ -57,7 +57,7 @@ func TestGoroutineManagerContextExpires(t *testing.T) {
 
 	m := NewGoroutineManager(ctx)
 
-	require.NoError(t, m.Go(func(ctx context.Context) {
+	require.True(t, m.Go(func(ctx context.Context) {
 		<-ctx.Done()
 	}))
 
@@ -80,7 +80,7 @@ func TestGoroutineManagerContextExpires(t *testing.T) {
 	}
 
 	// Make sure new goroutines do not start after context expiry.
-	require.ErrorIs(t, m.Go(func(ctx context.Context) {}), ErrStopping)
+	require.False(t, m.Go(func(ctx context.Context) {}))
 
 	// Stop will wait for all goroutines to stop.
 	m.Stop()
@@ -108,11 +108,11 @@ func TestGoroutineManagerStress(t *testing.T) {
 	// implementation, this test crashes under `-race`.
 	for i := 0; i < 100; i++ {
 		taskChan := make(chan struct{})
-		err := m.Go(func(ctx context.Context) {
+		ok := m.Go(func(ctx context.Context) {
 			close(taskChan)
 		})
 		// If goroutine was started, wait for its completion.
-		if err == nil {
+		if ok {
 			<-taskChan
 		}
 	}
@@ -134,10 +134,10 @@ func TestGoroutineManagerStopsStress(t *testing.T) {
 	jobChan := make(chan struct{})
 
 	// Start a task and wait inside it until we start calling Stop() method.
-	err := m.Go(func(ctx context.Context) {
+	ok := m.Go(func(ctx context.Context) {
 		<-jobChan
 	})
-	require.NoError(t, err)
+	require.True(t, ok)
 
 	// Now launch many gorotines calling Stop() method in parallel.
 	var wg sync.WaitGroup