FIX: explicitly set the number of items that should appear in the hea…

…der.

This suppresses a dropdown from kicking in after 5 items, effectively creating a dropdown with only 1 item.
Instead, this just shows all 6 items in the header bar.

Closes mne-tools#1295 , which raised an issue with the rendering of the dropdown. If a dropdown is ever introduced again, this issue may rear its head again.

doc/conf.py

@@ -124,6 +124,11 @@
 html_static_path = ["_static"]
 html_css_files = ["style.css"]
 
+# The number of items that will appear in the header before the dropdown menu kicks in
+html_theme_options = {
+  "header_links_before_dropdown": 6,
+}
+
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
 # documentation.