Inconsistent drive letter case on Windows

Bug report + suggested fix

The os.path.abspath method on windows is inconsistent when pre-pending the drive letter as it can be either upper or lowercase.

It is not entirely clear from Microsoft's documentation (https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getfullpathnamew) when this happens exactly, but, a simple way of re-producing the issue is by changing directory and specifying the opposite case letter in the call

C:\Users\kieran>python -c "import os; print(os.path.abspath('.'))"
C:\Users\kieran

C:\Users\kieran>cd c:\Users\kieran\Projects

c:\Users\kieran\Projects>python -c "import os; print(os.path.abspath('.'))"
c:\Users\kieran\Projects

This is very frustrating when trying to compare paths, and, sometimes different tools in the same development environments will run in such a way that they change their drive letter case, leading to issues between those tools or differences inside tests.

I would like to suggest that we enforce the lowercase driver letters by making a small change to https://github.com/python/cpython/blob/0fe61d0838218b18bcff4bf434beba3e8dbcc42b/Modules/posixmodule.c#L4236-L4274

If we were to include an iteration (line 4266) of the buffered path that lowercased the chars up to the colon (guaranteed to be set), this would ensure consistent drive letters.

Your environment

Python 3.9.6
Microsoft Windows 10 Pro - 10.0.19044 Build 19044
x64-based PC

先從 Modules/posixmodule.c 中連結行附近的 Windows 路徑處理程式碼開始，然後使用報告中的 os.path.abspath 命令重現該行為。確認如何取得磁碟機代號，並將 Windows 絕對路徑中的磁碟機代號大小寫一致且相關行為由測試涵蓋定義為完成。