python: open UtilConfig files as binary

Problem: The Python 3.11 tomllib implementation requires that toml
files be opened in binary mode, but the UtilConfig class opens files
in normal read mode, resulting in a TypError

 File must be opened in binary mode, e.g. use `open('foo.toml', 'rb')`

Open all UtilConfig config files with mode 'rb'. This doesn't seem
to cause an issue with other config file types.

Fixes #5154

Author: grondo

src/bindings/python/flux/util.py

@@ -1042,7 +1042,7 @@ def load(self):
                     continue
 
                 try:
-                    with open(filepath) as ofile:
+                    with open(filepath, "rb") as ofile:
                         conf = self.extension_handlers[ppath.suffix](ofile)
                 except (
                     tomllib.TOMLDecodeError,