Fix layout regression in sidebar

Summary: D27233899 (dd1f2fdeaa) caused a layouting regressions. Fixed in this diff. Fixes https://fb.workplace.com/groups/flippersupport/permalink/1104019500078707/

Reviewed By: passy, fabiomassimo

Differential Revision: D27394188

fbshipit-source-id: d928c9da82beb850ff512393cbb589f625889442

desktop/flipper-plugin/src/ui/Sidebar.tsx

@@ -41,6 +41,7 @@ const SidebarContainer = styled(Layout.Container)<{
         backgroundColor: theme.backgroundDefault,
       }),
   flex: 1,
+  overflow: 'hidden',
 }));
 SidebarContainer.displayName = 'Sidebar:SidebarContainer';