Update icon to long arrow

Changelog: changed

app/views/shared/issuable/_sidebar.html.haml

@@ -97,7 +97,7 @@
       - if issuable_sidebar.dig(:current_user, :can_move)
         .block.js-sidebar-move-issue-block
           .sidebar-collapsed-icon{ data: { toggle: 'tooltip', placement: 'left', container: 'body', boundary: 'viewport' }, title: _('Move issue') }
-            = custom_icon('icon_arrow_right')
+            = sprite_icon('long-arrow')
           .dropdown.sidebar-move-issue-dropdown.hide-collapsed
             %button.gl-button.btn.btn-default.btn-block.js-sidebar-dropdown-toggle.js-move-issue{ type: 'button',
               data: { toggle: 'dropdown', display: 'static', track_label: "right_sidebar", track_property: "move_issue", track_action: "click_button", track_value: "" } }