Fix File.dirname with unicode chars

[asterite]

Fixes #8910

There are a lot of + 1 in the code that might be worth reviewing. If someone wants they can try adding unicode tests to all of the File or Path methods to make sure they work well.

[straight-shoota]

Ooops.

[straight-shoota]

I'll take a look at all implementations to make sure they work with unicode strings.

[straight-shoota]

The rest of Path seems to be good. We could consider adding lots of specs with unicode paths to make sure there won't be any issues in the future.

[asterite]

@straight-shoota Thank you for checking! If everything is good then I think we don't need to add those tests.

[Sija]

@straight-shoota Thank you for checking! If everything is good then I think we don't need to add those tests.

@asterite Well, it's good for now, we just need to subtly break the implementation to find out we need these tests anyway, so why wait for it if we can be prepared? 👑

[straight-shoota]

Yes, having such test would be great. But it requires also quite some effort to implement and review. IMO that effort is currently better put to use elsewhere.