convert: turn the last str regex into bytes in cvs.py (issue6789)

Since root is bytes, the regular expression should also be bytes.

hgext/convert/cvs.py

@@ -142,7 +142,9 b' class convert_cvs(converter_source):'
 
         if root.startswith(b":pserver:"):
             root = root[9:]
-            m = re.match(r'(?:(.*?)(?::(.*?))?@)?([^:/]*)(?::(\d*))?(.*)', root)
+            m = re.match(
+                br'(?:(.*?)(?::(.*?))?@)?([^:/]*)(?::(\d*))?(.*)', root
+            )
             if m:
                 conntype = b"pserver"
                 user, passw, serv, port, root = m.groups()