[FIX] portal: color issue in user dropdown

Prior to this commit, icons in the user dropdown were not visible when
we applied a dark background color on the header.
In fact, when we use a dark background, it applies the "nav-dark" style
and turns the "text-muted" in a light gray which is not visible on white
background.

This commit fixes this issue by using the primary color instead of the
muted gray.

task-3060986

Part-of: odoo/odoo#119650

addons/portal/views/portal_templates.xml

@@ -122,11 +122,11 @@
                 </a>
                 <div t-attf-class="dropdown-menu js_usermenu #{_dropdown_menu_class}" role="menu">
                     <a groups="base.group_user" href="/web" role="menuitem" class="dropdown-item ps-3" id="o_backend_user_dropdown_link">
-                        <i class="fa fa-fw fa-th me-1 small text-muted"/> Apps
+                        <i class="fa fa-fw fa-th me-1 small text-primary"/> Apps
                     </a>
                     <div id="o_logout_divider" class="dropdown-divider"/>
                     <a t-attf-href="/web/session/logout?redirect=/" role="menuitem" id="o_logout" class="dropdown-item ps-3">
-                        <i class="fa fa-fw fa-sign-out me-1 small text-muted"/> Logout
+                        <i class="fa fa-fw fa-sign-out me-1 small text-primary"/> Logout
                     </a>
                 </div>
             </li>
@@ -694,7 +694,7 @@
     <template id="my_account_link" name="Link to frontend portal" inherit_id="portal.user_dropdown">
         <xpath expr="//*[@id='o_logout_divider']" position="before">
             <a href="/my/home" role="menuitem" class="dropdown-item ps-3">
-                <i class="fa fa-fw fa-id-card-o me-1 small text-muted"/> My Account
+                <i class="fa fa-fw fa-id-card-o me-1 small text-primary"/> My Account
             </a>
         </xpath>
     </template>