Fix create issue dropdown button wrapping

Display flex class was being overtaken by some nav
classes, so replace it with the important variant
Also remove button so buttons are evenly spaced
on the issue list page

Changelog: fixed

app/views/shared/_new_project_item_select.html.haml

 - if any_projects?(@projects)
-  .project-item-select-holder.btn-group.gl-ml-auto.gl-mr-auto.gl-py-3.gl-relative.gl-display-flex.gl-overflow-hidden
+  .project-item-select-holder.btn-group.gl-ml-auto.gl-mr-auto.gl-relative.gl-overflow-hidden{ class: 'gl-display-flex!' }
     %a.btn.gl-button.btn-confirm.new-project-item-link.block-truncated.qa-new-project-item-link{ href: '', data: { label: local_assigns[:label], type: local_assigns[:type] }, class: "gl-m-0!" }
       = loading_icon(color: 'light')
     = project_select_tag :project_path, class: "project-item-select gl-absolute! gl-visibility-hidden", data: { include_groups: local_assigns[:include_groups], order_by: 'last_activity_at', relative_path: local_assigns[:path], with_shared: local_assigns[:with_shared], include_projects_in_subgroups: local_assigns[:include_projects_in_subgroups] }, with_feature_enabled: local_assigns[:with_feature_enabled]