pyproject.toml exclude needs validation or better type handling

[daggaz]

When defining a pyproject.toml with the exclude option, and not understanding that it must be a list, people (me) write things like:

[tool.diff_cover]
exclude = "some/file.py"

Because strings are iterable, this ends up here, calling fnmatch() on each item in ['s', 'o', 'm', 'e', '/', 'f', 'i', 'l', 'e', '.', 'p', 'y'].

Very confusing.

And when you include a * that ends up always excluding everything, which make you think you've succeeded, when in fact you just entirely disabled the tool.

I think that it should either be an error to pass a plain string, or perhaps more helpfully adding if isinstance(patterns, str): patterns = [patterns], allowing both exclude = "string" and exclude = ["strings"].

[Bachmann1234]

Try version 10.0.0 #561

Major version bump is because I dropped support for python 3.9 as its end of life