fluent 2 - fix spinner flyout

src/Avalonia.Themes.Fluent2/Controls/ButtonSpinner.xaml

@@ -178,6 +178,7 @@
                           <ControlTheme TargetType="FlyoutPresenter" BasedOn="{StaticResource {x:Type FlyoutPresenter}}">
                             <Setter Property="Padding" Value="0"/>
                             <Setter Property="Background" Value="Transparent"/>
+                            <Setter Property="MinWidth" Value="0"/>
                           </ControlTheme>
                         </Flyout.FlyoutPresenterTheme>
                         <Border Name="PopupContentRoot"