Fix `ntpath.normpath()` for drive-relative paths

[nineteendo]

Bug report

Bug description:

from @eryksun (#117855 (comment)):

Note that the behavior for normalizing drive-relative paths is currently wrong in this case on Windows:

>>> nt._path_normpath('C:./spam')
'C:.\\spam'

That's the result that we want here when returning an explicit current directory for internal use, but that's not the expected behavior for normpath(). The fallback implementation that's used on POSIX gets it right:

>>> ntpath.normpath('C:./spam')
'C:spam'

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

• gh-126780: Fix ntpath.normpath() for drive-relative paths #126801
• [3.13] gh-126780: Fix ntpath.normpath() for drive-relative paths (GH-126801) #127103