doc: link-roles: Update path handling to use document name

Use docname instead of source from get_source_and_line() because
source can be a relative path to an included file (e.g., .rst.inc),
while docname is always the main document being processed.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

doc/_extensions/zephyr/link-roles.py

@@ -119,7 +119,8 @@ def modulelink(default_module=None, format="blob"):
             )
 
         if module == config.link_roles_manifest_project:
-            p = Path(source).relative_to(inliner.document.settings.env.srcdir)
+            docname = inliner.document.settings.env.docname
+            p = Path(docname)
             if (
                 not any(
                     p.match(glob)