fix tab key for lyric box

Author: stakira

OpenUtau/Controls/LyricBox.axaml

@@ -19,7 +19,7 @@
                BorderThickness="0" Background="Transparent"
                Margin="{DynamicResource AutoCompleteListPadding}"
                ItemsSource="{Binding Suggestions}" SelectedItem="{Binding SelectedSuggestion}"
-               KeyDown="ListBox_KeyDown">
+               Focusable="True" KeyDown="ListBox_KeyDown">
         <ListBox.Styles>
           <Style Selector="ListBoxItem">
             <Setter Property="Padding" Value="0"/>