Do not generate dropdown in sidebar.

This should fix pydata#1735, it is complementary to pydata#1564 but with a different
approach.

Instead of generating the same navbar as the fullpage width one, it
generate one with no dropdowns, with this, any css that tries to make
downtown looks like normal links in html becomes unnecessary.

src/pydata_sphinx_theme/theme/pydata_sphinx_theme/sections/sidebar-primary.html

@@ -6,7 +6,13 @@
     {% if theme_navbar_center %}
       <div class="sidebar-header-items__center">
         {% for navbar_item in theme_navbar_center %}
-          <div class="navbar-item">{% include navbar_item %}</div>
+          {#
+            we are in the sidebar for narrow screnns for example, we do not want
+            an dropdown, so set the max drop value to a large number Here 999.
+          #}
+          {% with theme_header_links_before_dropdown=999 %}
+            <div class="navbar-item">{% include navbar_item %}</div>
+          {% endwith %}
         {% endfor %}
       </div>
     {% endif %}

src/pydata_sphinx_theme/toctree.py

@@ -2,7 +2,7 @@
 
 from functools import cache
 from itertools import count
-from typing import Iterator, List, Union
+from typing import Iterator, List, Tuple, Union
 from urllib.parse import urlparse
 
 import sphinx
@@ -101,8 +101,18 @@ def unique_html_id(base_id: str):
         return next(get_or_create_id_generator(base_id))
 
     @cache
-    def generate_header_nav_before_dropdown(n_links_before_dropdown):
-        """The cacheable part."""
+    def generate_header_nav_before_dropdown(
+        n_links_before_dropdown,
+    ) -> Tuple[str, List[str]]:
+        """Return html for navbar and dropdown.
+
+        Given the number of links before the dropdown, return the html for the navbar,
+        as well as the list of links to but in a dropdown.
+
+        Returns:
+            - HTML str for the navbar
+            - list of HTML str for the dropdown
+        """
         try:
             n_links_before_dropdown = int(n_links_before_dropdown)
         except Exception: