path-suboption: use str for "bookmarks_mode" suboptions

That second argument refer to an attribute and do not needs to be bytes.

mercurial/utils/urlutil.py

@@ -732,7 +732,7 b' SUPPORTED_BOOKMARKS_MODES = {'
 }
 
 
-@pathsuboption(b'bookmarks.mode', b'bookmarks_mode')
+@pathsuboption(b'bookmarks.mode', 'bookmarks_mode')
 def bookmarks_mode_option(ui, path, value):
     if value not in SUPPORTED_BOOKMARKS_MODES:
         path_name = path.name