Make it possible to handle toasts in integration tests

Use it in two selected tests to demonstrate what it looks like.

pkg/gui/types/common.go

@@ -144,6 +144,7 @@ type IPopupHandler interface {
 	WithWaitingStatusSync(message string, f func() error) error
 	Menu(opts CreateMenuOptions) error
 	Toast(message string)
+	SetToastFunc(func(string))
 	GetPromptInput() string
 }