path-suboption: deprecated specifying the attributes as bytes

The known suboptions have been updated, so we can deprecated passing bytes in case
some extensions use them.

mercurial/utils/urlutil.py

@@ -18,6 +18,7 b' from .. import ('
     error,
     pycompat,
     urllibcompat,
+    util,
 )
 
 from . import (
@@ -681,6 +682,10 b' def pathsuboption(option, attr, display='
     This decorator can be used to perform additional verification of
     sub-options and to change the type of sub-options.
     """
+    if isinstance(attr, bytes):
+        msg = b'pathsuboption take `str` as "attr" argument, not `bytes`'
+        util.nouideprecwarn(msg, b"6.6", stacklevel=2)
+        attr = attr.decode('ascii')
 
     def register(func):
         _pathsuboptions[option] = (attr, func)