Add missing .include-dark to nav-breadcrumbs image

The dark variant (nav-breadcrumbs-dark.png) was already in the PR but
the .qmd reference was missing the .include-dark class.

Author: cderv

docs/websites/website-navigation.qmd

@@ -401,7 +401,7 @@ website:
 
 The page `tutorials.html` contains the following breadcrumb:
 
-![](images/nav-breadcrumbs.png){.border fig-alt="Screenshot of a webpage. Above the header 'Tutorials' is the linked text 'Tutorials > Tutorial Landing'." width=50%}
+![](images/nav-breadcrumbs.png){.border .include-dark fig-alt="Screenshot of a webpage. Above the header 'Tutorials' is the linked text 'Tutorials > Tutorial Landing'." width=50%}
 
 You can disable breadcrumbs for a website using the `bread-crumbs` option: