Remove casefold since it doesn't exist on bytes (and the code needs t…

…o work with str and bytes)

Lib/shutil.py

@@ -1560,8 +1560,8 @@ def which(cmd, mode=os.F_OK | os.X_OK, path=None):
         # for a PATHEXT match. The first cmd is the direct match
         # (e.g. python.exe instead of python)
         # Check that direct match first if and only if the extension is in PATHEXT
-        suffix = os.path.splitext(files[0])[1].casefold()
-        if mode & os.X_OK and not any(suffix == ext.casefold() for ext in pathext):
+        suffix = os.path.splitext(files[0])[1].upper()
+        if mode & os.X_OK and not any(suffix == ext.upper() for ext in pathext):
             del files[0]
     else:
         # On other platforms you don't have things like PATHEXT to tell you