Add patching getcwd/getcwdb for nt

[mrbean-bremen]

• fixes Windows problem if called from fspath, if the real current drive is not C:
• fixes test for patch_open_code doesn't seem to work in Python 3.12 #892 under Windows

Turns out that the fix for #892 actually worked, but with the concrete test code it failed under Windows in the CI because the current working dir was on another drive than C:.
The notation with a slash (or backslash) at the beginning of the path under Windows means that it uses the current drive. On creating the path, the current drive in the fake fs was used (which is C: by default) by calling getcwd in the fake fs, but importlib.util.spec_from_file_location used os.fspath that under Windows uses nt.getcwd instead of os.getcwd, which was not patched.
Patching nt.getcwd fixes this.

Tasks

• Unit tests added that reproduce the issue or prove feature is working
• Fix or feature added
• Pre-commit CI shows no errors
• Unit tests passing