setup.py: fix version parsing on Python 3.14 (ast.Str removed)

[sookach]

Python 3.14 removes the ast.Str node type. String literals now appear as ast.Constant(value=str).
Update the AST check to accept both ast.Str (for older Pythons) and ast.Constant with a string value (for Python 3.8+), allowing html5lib to build successfully on Python 3.14 while remaining compatible with older version. Tested at desk with pip install -e .

Fixes: #588

[atsampson]

This isn't right for pre-3.14 versions - the version = line fails because there's no a.value.value on older versions. Something like this works (tested on 2.7 and 3.11-3.14):

version = None
with open(join(here, "html5lib", "__init__.py"), "rb") as init_file:
    t = ast.parse(init_file.read(), filename="__init__.py", mode="exec")
    assert isinstance(t, ast.Module)
    assignments = filter(lambda x: isinstance(x, ast.Assign), t.body)
    for a in assignments:
        if (len(a.targets) == 1 and
                isinstance(a.targets[0], ast.Name) and
                a.targets[0].id == "__version__"):
            if hasattr(ast, "Str") and isinstance(a.value, ast.Str):
                version = a.value.s
            elif (hasattr(ast, "Constant")
                  and isinstance(a.value, ast.Constant)
                  and isinstance(a.value.value, str)):
                version = a.value.value
assert version is not None

[sookach]

Thanks! Updated the PR.