docs/sphinx: Explicitly convert Sphinx paths to str

Sphinx 7.2+ is switching to using pathlib.Path
instead of str to represent paths. This fixes the
current deprecation warnings and eventual breakage.
This conversion will be a no-op when using older
Sphinx versions.

Signed-off-by: Oliver Faso <erer1243@gmail.com>
Tested-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20230910040811.53046-1-erer1243@gmail.com
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/sphinx/kfigure.py b/doc/sphinx/kfigure.py
index 7887048..dea7f91 100644
--- a/doc/sphinx/kfigure.py
+++ b/doc/sphinx/kfigure.py
@@ -266,7 +266,7 @@
     if dst_fname:
         # the builder needs not to copy one more time, so pop it if exists.
         translator.builder.images.pop(img_node['uri'], None)
-        _name = dst_fname[len(translator.builder.outdir) + 1:]
+        _name = dst_fname[len(str(translator.builder.outdir)) + 1:]
 
         if isNewer(dst_fname, src_fname):
             kernellog.verbose(app,