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ntpath.splitroot raises UnicodeDecodeError when given bytes on Windows #122143

Description

@tjensen

Bug report

Bug description:

The ntpath.splitroot function appears to have changed in Python 3.13 such that it now raises a UnicodeDecodeError when the given pathname is a bytes containing invalid Unicode characters, but only when running on Windows:

Python 3.13.0b4 (tags/v3.13.0b4:567c38b, Jul 18 2024, 10:14:53) [MSC v.1940 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import ntpath
>>> ntpath.splitroot(b"foo\x88")
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    ntpath.splitroot(b"foo\x88")
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x88 in position 3: invalid start byte

The same code works without raising on Windows when using Python 3.12:

Python 3.12.4 (tags/v3.12.4:8e8a4ba, Jun  6 2024, 19:30:16) [MSC v.1940 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import ntpath
>>> ntpath.splitroot(b"foo\x88")
(b'', b'', b'foo\x88')

The same code also works without raising on Linux when using Python 3.13 or 3.12:

Python 3.13.0b4 (main, Jul 22 2024, 17:26:46) [GCC 13.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import ntpath
>>> ntpath.splitroot(b"foo\x88")
(b'', b'', b'foo\x88')
Python 3.12.4 (main, Jun 15 2024, 10:31:39) [GCC 13.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import ntpath
>>> ntpath.splitroot(b"foo\x88")
(b'', b'', b'foo\x88')

CPython versions tested on:

3.12, 3.13

Operating systems tested on:

Linux, Windows

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    3.13bugs and security fixes3.14bugs and security fixesOS-windowsextension-modulesC modules in the Modules dirstdlibStandard Library Python modules in the Lib/ directorytype-bugAn unexpected behavior, bug, or error

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