Fix Paths.IsInsideDir method when paths belongs to different drives/filesystem

[cmaglie]

When comparing two paths from different drives like:

a := paths.New(`C:\AAA\BBB`)
b := paths.New(`D:\AAA\BBB\CCC`)
fmt.Println(b.IsInsideDir(a))

the function IsInsideDir returns an error instead of the correct result false.
See arduino/arduino-cli#2156 for a real-world use case.