Fix secondary header menu items stacking vertically (#794)

Bootstrap 5's .navbar-nav sets flex-direction: column by default,
which overrides the float: left on list items. Add flex-direction: row
to #secondary-header ul.menu so items display inline.

Fixes #793

Co-authored-by: Jurriaan Roelofs <jur@dxpr.com>

Author: jjroelofs

css/components/dxpr-theme-secondary-header.css

@@ -28,6 +28,7 @@
   }
 
   ul.menu {
+    flex-direction: row;
     float:right;
     margin-bottom: 0;
     margin-top: 0;