Increase RTD's navigation depth from 4 to 5

To match the level we had de facto before merging devel/sysadm/user
into a single tree

swh/docs/sphinx/conf.py

@@ -111,6 +111,7 @@ html_favicon = "_static/favicon.ico"
 #
 html_theme_options = {
     "collapse_navigation": True,
+    "navigation_depth": 5,
     "sticky_navigation": True,
     "titles_only": True,
 }