on windows, path comparison should be case-insensitive

[ThomasWaldmann]

Just seen that on github CI (windows / msys2 based part), using the latest setuptools_scm:

WARNING setuptools_scm._file_finders.git toplevel mismatch computed d:/a/borg/borg vs resolved D:/a/borg/borg 

[RonnyPfannschmidt]

@ThomasWaldmann seems like we are hitting python/cpython#84548

i'll investigate a workaround