Fix a border case for local fs copy from local

[tramora]

Fix a border case in the LocalFileSystem.copy_from_local where a relative path is given for the target file.

The library would try and fail to create a parent directory named ''

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[popescu-v]

See the comment.

[popescu-v]

See the remaining comment.

[popescu-v]

IMHO, we could also use pathlib.Path(target_file_name1).unlink(missing_ok=True), which seems simpler and more explicit to me.

[tramora]

Improved

[popescu-v]

LGTM, but a further simplification can be made in the tests (see comment).