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>

doc/sphinx/kerneldoc.py

@@ -138,7 +138,7 @@ class KernelDocDirective(Directive):
                     lineoffset = int(match.group(1)) - 1
                     # we must eat our comments since the upset the markup
                 else:
-                    doc = env.srcdir + "/" + env.docname + ":" + str(self.lineno)
+                    doc = str(env.srcdir) + "/" + env.docname + ":" + str(self.lineno)
                     result.append(line, doc + ": " + filename, lineoffset)
                     lineoffset += 1